Everyday Scientist

2009-09-04T18:01:00.007-05:00

Preservation of Trilobites

P. R. Sheldon (Lethais v.21, p293-306, 1988) notes that the genus Ogyginus from shales and also Llanvirn sandstones at Gilwern Hill Quarry are an exception to the local rule that trilobite pygidial width defines a normal or slightly bimodal unskewed distribution dominate by the final or holaspid stage of growth. According to him the Ogyginus corndensis (Murchison) from Gilwern Hill are “extremely abundant:, and in a previously collected museum collection of 463 intact specimens showed a maximum width of about 97 mm and some 335 specimens in the less than 13 mm width range of small holaspids and merapids (Trilobites by R. Levi-Setti (1993 Univ. of Chicago Press), the head merely being truncated during previous splitting of the poorly defined bedding planes. But the similar-looking, later Ordovician trilobite (Hall) does look abundant on shell beds separated by four mm thick layers of barren oil shale of the Collingwood Member of the Lindsay Formation, on the beach at Craigleith Ontario. But in this case the largest specimens are so fragmented and separated into particular layers that they are not collected or illustrated like the 20 to 45 mm specimens seen in Levi-Setti (pls. 3 and 136), H.B. Whittington ( Trilobites 1992, Boydell Press U.K.) and R. Ludvigsen (Fossils of Ontario, Part 1: The Trilobites Royal Ontario Museum 1979) from that particular site seen on my own photographs

Weberides mucronatus (McCoy) Acre Limst.

Calcareous shales overlying the Mississippian Acre Limestone, 300 m W.S.W. of Cullernose Point U.K. showed ten pygidia and one similarly disarticulated cranidium of Weberides mucronatus (McCoy) in a cluster with an equal number of brachiopods including still articulated, pyrite-filled Rugosochonites Sokolskaya, three small gastropods, one bivalve and four crinoid stem segments. Most of them are seen on the photographed half of the split bedding plane, which is probably the lower surface of the top judging from the greater oxidation of the pyrite on that side. The Pygidium marked b was therefore originally being deposited concave-up like the adjacent relatively smooth glabella seen aligned parallel to it. These shales represent a relatively near-shore marine environment, the trilobites being absent in basins. The cluster was presumably formed by waves despite the probable concave-up orientations. The pygidium marked b has a width and length around 11 mm and has broken through the calcite exoskeleton of 0.08 to 0.10 mm thickness producing a rather poor preservation on both the part and counterpart. The other trilobites were of similar size as are the brachiopods, supporting the idea of current sorting. This would explain the absence of thoracic segments presumably decayed into long harrow strips before the storm.

Pseudogygites latimarginatus (Hall) &Isorthoceras tenuistriatum(Hall) Craigleith Ont.Fragment of pygidium of larger size of 0.3 mm thickness, with same 0.05 mm pits and marginal wrinkles.
Pseudogygites & Isorthoceras, Craigleith Ontario

This and other shell layers of the Ordovician (Maysvillian) Linsay Formation on the beach at Craigleith, Ontario, are separated by three mm thick bands of relatively barren oil shale within the Collingwood Member. Two books entitled trilobites by H. B. Whittington (Boydell Press 1992) and R. Levi-Setti (Univ. of Chicago Press 1993) and also R. Ludvigsen’s Fossils of Ontario Part 1:The Trilobites (Royal Ontario Museum 1979) illustrate specimens of Pseudogygites latimarginatus (Hall) from this site with widths of the tail-plate of up to about 45 mm, but one from Bowmanville in a slightly different facies is seen on plate 136 of Levi-Setti with a greater width of about 61 mm on the tail-plate and about 68 mm on the associated thorax. It would seem from my photographs that specimens of that size are common at Craigleith, but being more disarticulated are seldom photographed. Since it is possible that such breakage is due to cephalopod predation, followed by resedimentation into basinal shell layers, rather than by molting as Ludvigsen proposed for the samll molts there, it is instructive to study exactly what these fragments look like. The associated orthoconic cephalopod Isorthocreas tenuistriatum (Hall), revised from Geisonoceras by R. C. Frey (U.S.G.S. Prof. Pap. 1066-P, p, P59, 1995) is too small to have attacked the adult trilobitesand is represented by a fragment of similar thickness (0.4 mm) to the tail-plate on the edge of the photograph with a similar width to the black separate thorax segment of 40 mm width.

Isorthoceras tenuistriatum (Hall) of 0.4 mm thickness with 0.1 mm transverse growth ridges
Pseudogygites separated fixed cheeks on glabella, Craigleith.

This photograph shows a pair of head fragments consisting of the fixed cheek on one side joined to the posterior axial segments of the cephalon with the other fixed cheek broken off before deposition. The posterior border of the axial segment of the larger fragment appears to be distorted perhaps because it was bitten earlier in life or because it was not fully calcified when attacked. The axial lobe width suggests the head was originally about 60 mm wide. The notch in the edge of the fixed cheek is where the eye separated molting along the facial suture as proposed by Ludvigsen, but the separation of the head from the thorax, and the irregular breakage of the other fixed cheek are not due to molting in his hypothesis. The unusual feature is a posterior margin running at an angle to the segmentation of the head and not bending back at the mid-line.

Fake Calymene blumenbachii Brongniart, Dudley

Pygidium of 21 mm width, 0.08 mm thick

Occipital ring with possible predation scar

Disarticulated thoracic segment of 40 mm width, with pleural furrows on pleural lobes flanking 10 mm wide axial lobe with 0.2 mm thick shell covered with 0.05 mm dorsal pits.

The Dudley Locust was collected when the Wenlock Limestone was mined there and often sold with the disarticulated fragments glued with local rock dust as whole specimens were rare and more expensive. This one looks odd because it lacked the free cheeks and an attempt by the collector or dealer to expose them, or perhaps find others to add there failed. The pygidium has been added in a fake matrix, which now has microscopic cracks in it, these parts being relatively common. The thorax therefore shows ten not 13 segments, divided into two sets of five, which do appear to belong together despite distortion,. However, there is a better type of glue/matrix along the sides suggesting that the thorax was added to the interesting cranidium with a probable cephalopod bite mark in the occipital ring.

Pleurobrachia - Part 2

2009-06-10T17:55:00.000-05:00

June 1, 2009

Given one change of the tank water from the sea on May 22, the Pleurobrachia continued to feed on the few available copepods until it was last seen alive at about noon on the 25th. Most of the time it lived at the surface with the two tentacles hanging below and then retracting, but when last seen it was moving down with the cillia beating and the tentacles extended below. On June 1st, the tank sediment was partly removed with the old water and appeared to preserve the corpse, which could not be seen before, as a grey triangular disc of 10 mm length extending upwards into a brown 60 mm filament in the water. It would seem that live Pleurobrachia remain at the surface by active swimming and then sink to die giving them some potential of becoming fossils despite being originally transparent and nearly all composed of water. When a Beröe cucumis Fabricus similarly arrived with the new water by accident on July 12, 2007, it was considerably more active, actively swimming up from the default position on the tank floor, where it presumably died within one day. That seawater did show flashes of light in the night, but they did not come from the moving Beröe and no light was seen at all in the Pleurobrachia water. Beröe are reported to appear later in the year because they eat Pleurobrachia, which can themselves live longer in the tank by feeding on copepods.

Sepia adults and Pleurobrachia at Southend-on-Sea

2009-05-31T18:16:00.004-05:00

May 18-20 2009
During the end of a long period of relatively cool and windy weather, coincident with relatively low high tides (neap), the strandlines of dead crabs, brown and recently grown green algae still lacked jellyfish (studied Shoebury to Leigh on 19th May). They did show an only slightly bird-peck-marked cuttlebone of 179 mm length, 68.3 mm width and 20.1 thickness, deposited by the morning tide of the 19th, with the posterior end pointing 102° E. of true north on the Westcliff strandline with that trend. A hundred m or so to the west, a corpse of a female cuttlefish was aligned with the posterior end pointing towards 94° E. of N. between two strandlines spaced about 0.6 m apart and trending 104°E. of N. Both specimens were dorsal-up, and the corpse had evidently arrived earlier during the two tides of similar, slightly higher height on May 18. When removed the shell had slightly large dimensions of 191 mm by 69.6 mm by 22.2 mm thickness. Both the thickness and the length of the last septum measured in the median plane are a good guide to the maturity and races of these adults Sepia officinalis L. and the last septa were respectively 66 mm and 72.5 mm long. It is possible that the smaller one was the male of a pair that had recently mated in the Zostera beds of Canvey Island, but the female still contained numerous 6 mm diameter oocytes in a 40 mm diameter posterior-dorsal ovary. The jaws had dimensions of 25.5 mm by 24.0 mm width and 10.5 mm by 32.3 mm. The two tentacles were largely gone and the arms contracted and or similarly degraded, producing stranded body dimensions of about 210 by 88 by 60 mm, which sank with the shell insitu and the head jack-knifed after 3.0 hours in seawater

A water sample taken after the morning tide of May 20 at Chalkwell, was of interest in containing a sea gooseberry Pleurobrachia pileus (O.F. Mueller) which was still alive in the tank on the 21st and attempting to feed from the poor animal food supply in the water sample, with the mouth at the waterline and the two tentacles with spreading lassoe cells

Stranding of Cuttlebones

Two more adult Sepia officinalis L. shells were stranded by the afternoon tide on June 8, 2009 within 8 km of strandline from Leigh to Thorpe Bay, probably after local spawning. The posterior end of one shell with dimensions of 181 by 71.4 by 21.4 mm (septum 78 mm long) was pointing 179° E. of N., 0.3 m from the edge of the wet sand trending 94° E of N. The second shell, also from Southchurch, had dimensions of 164 by 64.9 by 19.4 mm (septum 72 mm long) and had a posterior end directed towards 121° E. of N., 0.6 from the limit of wet sand trending 99° and deposited by Force 3 winds blowing from 79° producing breaking waves roughly parallel to the wind flow. Both shells were dorsal-up with bird puncture marks ventrally. The successive orientations of the posterior end of the smaller cuttlebone were recorded as it was moved about 50 m westwards by the rising high tide before developing this higher final orientation partly covered by sand and gravel. The first three strandings were dorsal-up and defined a clockwise rotation of the posterior end 40, 20 and then 170° E. of N. at different sites in the sand slope of the swash zone. When in the waves the long axis was parallel to the wind and wave crests, but it flipped over into a ventral-up orientation from this more orthogonal orientation and then repeated another clockwise rotation defined by four ventral-up strandings around 60°, 130°, 160° and 200° E. of N. It then flipped back when out in the breaking waves and showed dorsal-up strandings of about 50°, 140° and 50° E. of N. on the sand slope, followed by 49°, 69° and then 121° on the gravel berm. Wet sand was initially 0.3 m beyond the 121° position and later spread to 0.6 m without moving it.

The 18 mm long radula of the stranded sepia showed a total of about 60 transverse rows of translucent chitinous teeth (‘’i.e.’’ not black like the parrot-like jaws around it, or yellowish brown like the chitinous hood and margins of the cuttlebone). The taxonomically stable feature of the radula is the seven longitudinal rows of sharp teeth and additional flat marginal plates, which in Sepia all lack the jagged denticulation of each tooth seen in most octopus, squid and ammonites. The width of the seven rows is 3 to 4 mm on the concave basal membrane and consist of a central radial tooth, flanked by three rows termed lateral one two and three of increasing lateral height.

Thornback Rays stranding at Southend – March 26, 2009

2009-04-26T15:16:00.002-05:00

The morning, stormy high tide at Chalkwell in Southend stranded a large ray on March 9, and the vertebra of this specimen, or more likely others, were found at Westcliff on March 11 and Southend on the 12th. The Afternoon tide of March 16 stranded an undecayed specimen, curved and ventral-up on the high water mark at Thorpe Bay. It was a Thornback Ray Raja clavata lacking the yellow tag put on by Cefas for their Thames Ray Tagging and Survival 2007 - 08 study (‘’www.cefas.co.uk’’). After that the tides were generally at a lower level on the beach, but when the strandline of the afternoon tide of March 26 was studied at about the same height, the ray was found to have been converted into a curved skeleton which had moved 140 m to the east and over one groyne. It was ventral-up and showed the thin teeth of males in a head skeleton width of 125 mm, and a now partly preserved overall length of 0.5 m. Presumably it was eaten by gulls on the beach and then moved by the ides as they returned to the same elevation.

Hummocky Cross Stratification

2008-11-10T18:56:00.003-05:00

Oct 7,2008

The photographs show a rectangular calcite cemented 0.15 m thick block of black laminated very fine grained sandstone interbanded with and cut by white bands and burrow fillings representing bioturbated clays deposited between offshore marine storms in the Eocene London Clay Formation. The block was dug up recently at a depth of 18 inches (c.0.5 m) in the front garden of Symonds Avenue in Eastwood, Essex, previously mapped by the British Geological Survey officer G.W. Green as basal Claygate Beds of Eocene age when it was a grassy field in 1972. More recently an excavation in the pavement there showed laminated orange sands and brown clays at the same depth and altitude (38 m above mean seal level). The occurrence of flint pebbles in the loose sands made it look like the local Quaternary Brickearth deposits showing similar banding elsewhere. Having a calcite cemented block of the sands, which include one 5 mm diameter quartz grain in the side, confirms the mapping of these sands as an uncontaminated Eocene storm deposit within the upper part of marine London Clay Formation. The way-up of the block was unrecorded and unclear, with fungal spores on the flatter side suggesting it was once on top in the soil and the cutting of the black sands by white clay-filled Eocene marine burrows (Chondrites and some larger ones) suggesting it is actually below. The other side of the block is absent and the adjacent part is fully bioturbated. It is probably the top of a rapidly deposited storm sand layer buried within offshore marine clays. The sandy sedimentary structures look like Hummocky Cross Stratification (HCS).

Profile of gravel ridge near dead gull in Thorpe Bay

2008-03-04T19:30:00.001-05:00

Dead Gull stranded Thorpe Bay

2008-03-04T19:28:00.001-05:00

Dead Common Gull, Thorpe Bay, Feb 8, 2008

Gull corspe stranded on East Beach

2008-03-04T19:25:00.002-05:00

Gull bones with wing feathers stranded S. Side of Boom, Feb. 8, 2008

Western End of the Old Ranges Shoeburyness

2008-03-04T19:22:00.001-05:00

View 600 m E. to Barge Pier of 1909 used to disembark first British atomic bombs June 5-6 1952 S Shoebury Common.

2007 Council notice viewed from S. on Central East Beach cliffs.

2008-03-04T19:20:00.001-05:00

2005 Shoebury East Beach, Dale Knapping's Malm Burrs c.1860.

2008-03-04T19:18:00.001-05:00

Shoebury East Beach 1930's signs on Rampart Road wall

2008-03-04T19:16:00.001-05:00

1935-9 notices on local malm brick wall of c.1860, Old Ranges, Rampart Rd.

New Anti-Boat Boom of 1950-2 Shoebury East Beach

2008-03-04T19:13:00.002-05:00

Looking along the New Boom at high tide.

The New Boom from Blackgate Road Shoebury.

2008-03-04T19:11:00.001-05:00

c.2000 Council notice on New Ranges Fence, Pigs Bay

2008-03-04T19:08:00.002-05:00

Comparison of Rayleigh and Eastwood Churches

2007-02-08T08:06:00.000-05:00

December 22 2006. Measure all the London Clay concretions seen in the exterior of St. Lawrence and All Saints Church, Eastwood in Essex for comparison with Prittlewell Priory who held it as a chapel from about 1110 to the establishment of a rector in 1248. Probably this means that the Cluniacs were given what is now the Norman Nave built a few years earlier and that no further work was done with the tithes until the independent rector added the present Tower, Chancel and South Aisle walls, described as early 13th Century in architectural guidebooks. There are some later walls and an entirely red brick 16th Century South Porch which contain no London Clay materials; the bricks probably being made for sands and flint gravels of the second terrace mapped by the Geological Survey around the brook 0.3 to 1.1 km west of the church. These bricks have a similar colour on fresh faces (10R 6/6) to those made from well sorted coarse silts and very find sands of the Eocene Claygate Member in the Rayleigh South Porch, but contain obvious white and black pebbles in old bricks of dimensions 214 mm by 105 mm by 57 to 62 mm. Associated finer-grained bricks with dimensions 226 mm by 105 mm by 47 mm also have Pleistocene-derived flints in them. The Rayleigh South Porch is said to date from just before 1497 and has a granule-grade grog consisting of iron oxide concretions, yellow laminated sand clasts and similar sandy clay flakes; all of which could have come from the Claygate Member of the London Clay exposed around Rayleigh Church and Castle. The average and more uniform brick dimensions in that porch are 218 mm by 116mm by 58.5 mm. Previously measured Rochford Church tower bricks of similar age averaged 233 mm by 116 mm by 58.5 mm, and are derived from Pleistocene silts and sands in the Rochford Buried Channel under both Rochford and Eastwood Churches. At Rochford the coarse particles or grog included by the brickmakers consists of white and grey sandy clasts of dimensions 6 mm by 5 mm presumably made from calcareous concretions or previously dried silts of Pleistocene age. The Rochford tower was built for the grandfather of Anne Boleyn who died in 1515 and unlike the Eastwood and Rayleigh Churches his brickmakers made additional black bricks of similar size to produce diapers on the red brick tower. At Rayleigh this pattern was made in or shortly after 1515 by placing black flints among the Kentish Ragstones and septaria of the Alen Chapel, east chancel wall and some buttresses. It was not attempted in the South Porch probably because it was built before that fashion had developed and it was attempted at Eastwood.

Turning now to the London Clay concretions there is just one seen in the largely hidden walls of the Norman Nave. Since it contains no thick veins on the original exterior and differs in colour from those in the 13th Century walls it may perhaps be regarded as a questionable septarian record. The average colour measured from three parts of it in the freezing fog is 5.0YR 3.67/3.33 and in a previous visit in the bright afternoon weather of October 3 2005 it averaged 6.67 YR 4.00/3.33. Two parts of it were recorded as dark yellowish orange (10YR 6/6) and blackish red (5R 2/2) in both weather conditions by holding the Rock Colour Chart colours in the same light as the wall enveloped by the grey background cardboard of the chart. A third area of the concretion was recorded as Greyish Red (5R 4.2) in the sunshine and as the reddish brown (10R 3.2) today. With more experience I think that this concretion is from the London Clay, probably from Southend, and matches the red variety seen in Leigh Church tower, the Norman walls at South Church and Sutton churches and some of the Prittlewell Priory and Rayleigh Church septaria. By contrast the London Clay concretions in the Chancel and South Aisle at Eastwood are of a different colour and provinance with an average colour of their matrix measured today from 8 fragments and 24 areas of colour as 7.708 YR 6.208/3.33, changing to 7.692 6.269/3.341 with the addition of two vein colours seen on one of them (marginal prisms 5Y 8/1, central prisms of upsplit 4 mm thick vein 10 YR 6/6). Bearing in mind how small and scarce these concretion fragments were one should not assume that they do not come from thicker veined concretions seen at Southend, or were not bored by modern beach organisms. On December 14 and 18 I revisited Rayleigh Church and recorded all the colours on the London Clay concretions in the lower external wall of the most eastern of the four bays in the South Aisle, and also in what appears to be a later wall built around the post-1394 Ragstone tower forming a thicker west wall of the western bay to the South Aisle. The eastern bay include previously fallen concretion fragments showing Eocene high spired microgastropods (perhaps Litopia sp. or Spiratella tutulina (curry) and the west wall shows some calcite replaced wood with bivalve borings of Eocene age in it (3 mm diameter Teredolites longissimus Kelly and Bromley. The claystone matrix of the fallen fragments, of both grey unweathered and red veined lithology is full of coarse silt and very fine sand in a bioturbated clay matrix. The veins all have a pale yellow prismatic margin, followed by dark orange as at Eastwood, and then when thick enough another pale layer of open scalecohedral calcite prisms with a dark surface on the open vein. In one case this dark manganiferous oxide layer was overgrown by a 20 mm diameter rostette of white barite fibers, as at Prittlewell Priory. In terms of the average colours of the matrix and jointing in the western wall of the South Aisle was 2.22 Y 6.833/2.500 (18 determinations), the new insitu measurements of east bay 8.65 YR 6.294/3.024 (85 determinations) and the December 4 Choir Vestry 10.0 YR 6.229/3.057 (35 determinations). They all show the same sequence of veins and I do not doubt that all these walls were built from the same concretions, probably present on the site and perhaps left institu in the east bay wall when the church was repaired and extended in 1394. The sequence of vein cements is most characteristic at Rayleigh and obviously produced a variable average vein colour there recorded as follows: west wall (5) 9.00 YR 6.200/4.800. East Bay (20) 0.30Y 6.100/2.900, choir vestry (4), 2.50Y 7.500/3.000. This was an exposure of highly disturbed brown London Clay with similar thick-veined septaria of grey to brownish red colour on the upper beach about 110 metres east of Crowstone Avenue on December 20th and I intend to compare the samples to these similar-looking Rayleigh and Eastwood Church septaria over the holiday when dried.

Rock colours at Prittlewell Priory

2007-01-11T07:38:00.000-05:00

December 13 2006. Visited Prittlewell Cluniac Priory to check similarities between the septarian London Clay concretions formerly exposed in the foundations of the south transept of the Priory Church and those in the south aisle at Rayleigh Church potentially built before a rector was established there in 1314. Before that the Cluniacs of Prittlewell potentially had some involvement in Rayleigh Church. Around 1164 Thomas Beckett gave them some control over the Milton manor, (now Westcliff-on-sea and eastern Southend) which was held by the monks of Canterbury for their own supplies since 959 (Canterbury continuously Southchurch, presumably the coast east of the pier continuously since 823). The supplies doubtless included division D and perhaps E London Clay septaria used to rebuild the priory church in stone at the end of the 12th Century, after it was founded with no control over the coastal manors around 1110. This priory was dissolved in 1536. Since little local church building took place after that reformation until the Victorian era it is unlikely that any of the stones from the partly demolished priory can now be seen off the site. There is, however, an old, but post-1536 vintage wall showing the priory septaria in similar weathering conditions, on the north side of the cloister. Today I measured a north facing patch of these septaria and one or two in the cross-section of the wall using the Geological Society of America Rock Colour chart as at Rayleigh, Hadleigh, Broomfield etc. A patch if relatively wet and lichen-covered foundations near where the Chapter House passage would be in a monastery cloister (i.e. S.E.) was also measured and added to previous data from the now covered South Transept near the new wall (i.e.N.E.). The septarian veins were up to 11 mm thick and composed of prismatic calcite of variable lightness value and much less chroma than either the calcitic matrix of the host concretion margins or of the similarly thick and banded veins at Rayleigh. They do in fact match the scare septaria in the east nave at Hadleigh much better than the Rayleigh septaria and require a separate analysis of vein and matrix colours during averaging. Often there are hardly any vein surface colours to be seen in a church and their inclusion makes little difference to the average dominated by ferruginous sepatarian joint surfaces, weathered exteriors showing Eocene burrows and modern marine borings by Polydora and internal exfoliated calcite claystones. This is the case in the new and rather wet Chapter House passage concretions which averaged 7.576 YR 5.485/3.273 in a set of 33 colour determinations from all the orange concretions there. The undivided data from the new wall averaged 7.754 YR 6.217/3.174; with the lightness value 6.217 increased by factors such as drying and lack of lichen to the condition seen in church walls and dried polished sections. The chroma saturation of 3.174 is slightly less because the new wall contains a more varied sample of the concretions from the priory, and the hue is shifted from red to yellow because of them and the inclusion of the calcite veins in the data set (69 determinations).
It needs to be explained that hues re averaged by imagining that the yellow-red (YR) scale continues through all the hues in a manner that produces small then negative numbers in red haematitic oxidation surfaces (i.e. -5 for hue 5.0 R) and large positive numbers for reduced iron purple-blue colours (i.e. +65 for 5.0 PB). Since most of the concretions are brownish the average is in the YR scale; but it can shift into the yellow scale Y when the matrix is a largely unweathered olive grey colour and pure calcite vein surfaces are exposed. Hues reported as such and such Y should have ten added to them when plotted or compared with averages still in the zero to ten Yellow-Red scale.
Vein surface measurements exclude the barite rostettes in the middle of the septarian cracks, which provide important provinance, clues. In the South Transept sea-worn and Polydora orange (10YR 6/6) concretions had rostette diameters of 20 mm, compared to 22 mm for the one in a similar matrix in the South Aisle Rayleigh. However, the averaged vein colours in all the determinations from the Priory site are much closer to Hadleigh and showed no more barite today.

Hadleigh E Nave veins (2) 2.50 Y 7.50/3.00

Hadleigh E Nave matrix (14) 6.4 3 YR 5.57/3.57

Priory x wall veins (21) 1.905 Y 6.33/2.38

Priory x wall matrix (93) 6.720 YR 5.96/3.56

Rayleigh Choir Vestry veins (4) 1.125Y 5.57/2.75

Bivalve Borings at Rayleigh Church

2007-01-06T07:52:00.000-05:00

December 4 2006. Visited Holy trinity Church in Rayleigh, Essex to buy Christmas cards sold to fund restoration of the building by registered charity 1069853. Also determined more colours on the London Clay Formation calcite concretions there, giving 46 determinations from the relatively old South Aisle (averaging the yellowish grey 1.74Y 5.76/2.96 in Munsell system) and the younger walls of the early 16th Century porch, buttress and flint diapers, plus a north-west extension which is presumably of 18th or 19th Century age. These younger wall concretions average another yellowish grey 0.12Y 6.18/3.02 and look like a less exfoliated version of heterogeneous concretions seen in the South Aisle. Perhaps this is because parts of the old walls from inside the church were reused in these relatively small extensions. Both parts show poorly veined and numerically dominant concretions bored by the modern marine worm Polydora Ciliata Johnston (as at Broomfield Church reviewed earlier). Polydora is more conspicuous in the relatively unexfoliated concretions between the early 16th Century red bricks of the porch and buttresses. A South Aisle concretion, fallen from a decayed part of the wall not yet renovated, showed Polydora borings of 1.5 mm U-tube diameter and 12 mm length extending from a poorly veined joint which was once open on a foreshore or subtidal wavecut platform. What appeared at first sight to be holes left by missing pebbles proved to be modern bivalve borings of 18 mm length and at least 45 mm length. These showed concentric ridges transverse to their axis. These are not seen when pebbles are removed from a soft rock or concrete. In addition, there were a modern bryozoa, presumably Membanipora, grown inside of the bivalve cavity. The sequence of events evidently started with the exposure of a wavecut platform of the London Clay Formation with a band of the subhorizontal calcite concretions worn into a pitted surface rather than the raised Eocene silt burrow fillings of radial Glockeria (seen in porch) and 1.5 mm diameter shafts and polygons (seen in all later walls). The septarian cracks, which were probably not thickly veined in the bored concretions at Rayleigh, became open and calcite-free surfaces extending as an escarpment of the platform with both Polydora worms and probably Burnea bivalves boring horizontally into the stone with a generally uniform weathered colour determined dry as the typical greyish orange 10YR 7/4 seen in churches. the similarity of the colour on the horizontal exterior, previously protected by mortar in the wall, contrasts with a local region of the bored vertical crack showing evidence of reduction of oxygen in the form of a 4 mm thick layer of pale blue 5 PB 7/2 showing no deflection around the Polydora borings passing through it. Since the bivalves had died and had their homes slightly encrusted by bryozoa before the concretion was collected, it is likely that it was displaced by the sea into a muddy foreshore before it was picked up. Probably the original site was a lower foreshore channel with dangerous riptides and the collection site was an adjacent muddy beach. This setting would match The Street at Whitstable today but there may have been similar environments in Essex in Roman, Saxon or perhaps later times before the South Aisle was built (presumably in 13th Century) but from an older church materials still being used for the buttresses etc. in c 1510 and later extensions. This brief reconstruction does not refer to the other type of London Clay concretion present in the South Aisle and new N.E. corner, except as part of the average colours. These clearly came from the Upper London clay, most probably in division D at Southend, rather than division E in the Rayleigh brick and tile excavations of post-1400 vintage. They show thicker sepatarian veins with coarse prisms of ferroan calcite including a dark yellowish orange (10YR 6/6) layer flanked by less chroma, and forming a rough surface in the middle of the cracks that in one case shows small rostettes of barite (barium sulphate) of the size seen at beach level where the coast bends between Westcliff and Chalkwell. What is less clear is whether these true septaria if the upper London Clay came from the same source as the bored concretions at Rayleigh described above. There is no actual proof of middle London Clay fossils in Rayleigh, although there is at Prittlewell and Rochford Churches in the less thickly varied material. Glockeria is seen both in division D at Chalkwell and division B in Essex, and they apparently thin-veined bored concretion noted above may just have come from the tip of a large tabular one in which the full thickness of the calcite veins is not developed. Certainly many of the Rayleigh concretions with a drab and smooth exteriors are just parts of the thickly veined ones, with a coarse silt matrix more typical of burrow-fillings in division D or E than the Glockeria and crinoid concretions of division B. The extent to which the average colour reflects a mixture of two different provinances is unclear in this more complex church building.

Leaf fall and strandings at Southend

2007-01-04T13:06:00.000-05:00

November 27, 2006. After a windy week and previous night Chalkwell beach showed a gravel ridge formed in front of a strandline of algae and diverse deciduous leaves. They included a greenish yellow leaf of the Hawthorne Crataegus monogyna Jacquin, shed by one tree in my garden from November 14 to 18 this year, and from the same tree in 1997 from November 7 to 16. Smaller Hawthorn trees and hedges still retained many yellow leaves today and in previous years (1996 and 2005) they only started to fall on December 1st and had gone within a week. Static floatation tests on the December 2000 insitu and fallen Hawthorne leaves yielded average times of 0.6 and 0.7 days, little more than one tidal cycle duration and a maximum time in a sample of 59 of 2.40 days. In the rough sea environment there is probably a long enough flotation time for these and many other deciduous leaves to cross the Thames from the opposite Kent coast (6 km) when the wind is from that southerly direction. However Oak and some evergreen leaves (i.e. Holly, Ivy) can float for over a week in tests and can come from a greater distance down the River Thames and other estuaries before being sunk or stranded. These leaves are seen in smaller numbers on strandlines throughout the year, usually after rain and in the case of evergreens, probably because of dumping of garden waste in the Thames.

A diverse leaf assemblage was studied at Chalkwell on November 28 2003 by collecting a mass of stranded algae and picking all the leaves out of it. The 57 leaves included 14 oak (12 Quercus robur L. and 2 of the local forest species Q. petraea (Mattuschka) and 30 serrated elongated leaves which may have included the other local forest tree Hornbeam Carpinus betulus L. In addition, there were 3 leaves of Poplar (Populus) which probably came from a tree near the beach, 2 or 3 Maple (Acer campestre L. and single leaves of Willow (Salix) and Horsechesnut (Aesculus). These three are common ornamental and street trees in Southend-on-Sea but seemed unlikely to have been blown into the sea from these more distant trees by the gentle south and west winds developed on the night of November 27/28 2003. Maple, Horsechesnut and a Sycamore (or Plane Tree?) leaves were observed in the strandline today and seem unlikely to have come directly from the land into stronger onshore wind.

The question of whether these leaf fall and stranding observations illuminate global warming is problematical since the botany textbooks relate the change in colour and strength of the leaves to reduced day length not temperature (i.e. via the plant hormone auxin). Looking at the common Southend street trees today (Aescules) there was evidence of still green leaves on branches of otherwise bare trees adjacent to streetlights. On the other hand, there were many entirely bare trees situated beside the lights and some retaining some leaves further away. None of the trees, except those suffering from a new disease in Horsechesnut had lost leaves on November 4, although many were partly yellow and brown by that date. Probably temperature and previous dehydration has an effect additional to that due to day length, but it is difficult to make general observations.

Septaria at Hadleigh church, Essex

2006-11-25T15:21:00.000-05:00

November 10 2006. The Church dedicated to St. James-the-less in the middle of the A13 road at Hadleigh was visited today for comparison of the London Clay concretion colours with the northern Essex church visited a week before. They were both largely Norman structures but at Hadleigh the stone was largely transported over the Thames from Kent in the early exciting reign of King Stephan (c.1140); probably as a secular defense measure by the church authorities. The eastern and western ends of the church were respectively repaired with the same and some new stone in 1854 (following collapse of the semicircular apse) and 1949 (following 1934-45 aerial bombing). A greater obscuration of the original fabric is due to the construction of a vestry in 1928 outside the northwest nave and a small wooden south porch in the 18th Century. There is no external tower only a wooden one on interior nave posts.

The first circuit of the exterior showed only one possible London Clay concretion in the lower two metres of all the old walls. The second more careful circuit provided a sample of colour measurements from ten stones and during a restudy of these particular stones on a third circuit this sample was reduced to 16 colours determined from four stones near the eastern ends of the nave and 8 colours determined from four less clearly London Clay concretions in the south wall of the chancel and the S.W. region of the nave beyond the porch. That corner included a probable glacial erractic of silica cemented, non-Cretaceous sandstone, with dimensions of 450 mm by 450mm that were larger than the Cretaceous sandstones and siltstones blocks obtained from Kent. There were also a few somewhat smaller slabs of ferricrete (iron oxide cemented flint gravel) in the south and west nave.

The largest stone of clearly London Clay origin had exposed dimensions of 220 mm by 180 mm shaped by splitting a concretion along prismatic calcite veins of 5 mm maximum half-thickness flanked on both sides by dark grey to moderate red, originally pyritic joint surfaces (5R 4/1-5R 4/4). The matrix of finer-grained calcite cemented clay graded from this colour, through paler browns and oranges, to a worn rather than a bored exterior weathered yellowish grey (5Y 7/2). Adding what appear to be beach-worn pebbles of the claystone matrix, the average colour of 16 studied spots is 6.56 YR 5.813/3.500 of the Munsell Co. system (i.e. roughly yellowish orange). The provinance is not the same as Broomfield Church as the veins were thicker and more pyritic but it is still unclear whether it represents division A3 of the Reculver-Herne Bay coast in Kent, or the division D/E boundary septaria which can still be found in Hadleigh Cliffs below and east of the subsequently built castle. The sea-worn appearance of some of the stones is of course opposed to that idea since Hadleigh Castle has old marshland separating it from the sea. But if the Kentish stones were landed at the more convenient port of Leigh and had their oyster-shell mortar added there i.e. even now a few whole oyster shells can be seen in the apse) then this objection is overcome. The more doubtful additional 8 colour determinations from four rather less weathered, silty-looking angular stones averaged 1.25 Y 5.750/2.875, which is roughly yellowish to olive grey. If it is reasonable to add them the general average from Hadleigh Church only shifts to 8.12 YR 5.792/3.292, which is yellowish orange. I suspect that the whole modern oyster shells used to make the mortar between the Kentish ragstone and other imported superior building stones came from London Clay shorelines on both sides of the Thames estuary. Some septaria were therefore collected with the future mortars up until the end of Church building with the reformation. It is therefore worth looking for London Clay concretions and recording their weathered colours etc in South Essex walls which are not supposed to contain them in published descriptions. Conversely when the London Clay concretions are common enough to have been noticed by visitors with more general interests, then they probably came from specific sites along the Essex or Kent coastline where they were gathered as building stones in an earlier period ending around 1200. There alternative perspective might be that a few concretions were like the Roman brick and tile fragments also seen in small numbers at Hadleigh Church and most south Essex churches, and came from the use of Saxon or Roman buildings as quarries in stone-poor Essex lands. A third idea, which I think is less likely, is that the insitu septaria seen now in fields such as those near Hadleigh Castle, were formerly gathered as additional building stones from each manor. Much will depend on how stable London Clay slopes were in ancient times when ploughing and excavation work was less easy than in modern times. However, it is relatively easy to test this local hypothesis by comparing the colours and weathered textures of church concretions with those found locally today.

Angel Wing’s at Broomfield

2006-11-16T19:12:00.000-05:00

November 7 2006. During the visit to Broomfield Church in Essex last Friday, it was noticed that one cluster of London Clay concretions in the nave contained borings by the modern marine worm Poydora ciliata Johnstone not seen elsewhere at convenient elevations in the walls and associated in one 130 mm by 80 mm stone with 6 mm diameter bivalve borings and insitu shells. In eastern North America, this type of bivalve or clam are given the name Angel Wing, more by comparison with the six and elongated wing development reviewed in Isaiah 6 v.2 than more speculative Christmas card illustrations with two spread wings like a bird. The bivalves in the wall building stone had bored in when it was on the lower or middle foreshore of Essex or North Kent, with rough radial ribs extending to a diameter of 6 mm at the working face and a delicate concentric ornament of growth ridges extending towards the entrance for the shell length of at least 15 mm before the stone was collected in Roman, Saxon or earliest Norman times. A complete and fully investigated shell would probably have an additional pair of small shelly plates filling the gape between the valves at the working face, or alternatively a fused similar folded structure there. It was not clear to me which species was present as juvenile and partly hidden shells in the church. Bearing in mind the age of the wall and the lack of evidence of repairs at that spot it is unlikely that the American species Petricola pholadiformis Lamarck [False Angel Wing] needs to be carefully separated from the unrelated homeomorphic English Native species Barnea candida (L.) [White Piddock] allied to the American B. truncata say [Small Angel Wing]. Petricola was first noticed in the River Crouch Estuary of Essex in July 1890 (see N. Tebble British Bivalve Seashells (1966) p. 126). However there is also a smaller English species, which although looking wider than those in the wall are are, is known from the Kent coast and provides an alternative identification. This is Barnea parva (Pennant) [Little Piddock]. There are also larger species Pholoas dactylus L. [Common Piddock] and Zirfaea crispata (L.) which also bore into rocks in southern England but which look somewhat different to the church shells.

The host rock would once have been a large concretion embedded in the London Clay below and probably partly covered by modern mud or sand above. It was then split along natural joints and a few thin septarian calcite veins either by the sea, during collection or transport or more likely just before building of the nave. One can see that the wall consists of a regular size and shape of the stones, with similar-looking fragments of probably the same original concretion placed next to each other, and the Polydora bored surfaces concentrated at the one spot in the whole wall. Unlike many other Essex walls there are no large intact concretions, and no thick-veined or open-veined concretions present. Elsewhere in the nave and older part of the Chancel there are concretions split along sepatarian calcite veins with a half-thickness of up to 4 mm and more iron-stained prisms at the edge nearest to the calcite claystone matrix. But they are not common enough to be seen with the bored material and this suggests a source in the division B, or middle London Clay of Kent or Essex, where septarian veins are thin and sparse. However, since both veined and unveined concretions are termed septaria in archaeological accounts of Essex it is reasonable to use that name for London Clay concretions regardless of vein frequency. This stratigraphical deduction implies that the concretions were not gathered from the subsequently suitable habitat for boring bivalves in the Crouch estuary or indeed the Roach and on the Thames at Southend. These are all upper London Clay foreshore sites, termed division C to E, in which even a small sample of concretions soon shows some thicker and or more open septarian veins. At Southend one can certainly find Polydora borings but often they and other marine animal traces are so common as to make the original surface features of the concretion hard to observed. This is particularly the case with museum specimens of division B dredged-up from subtidal environments at Clacton and Whitstable in early Victorian times. In all probability this mode of collection was not known to people in Roman or Saxon times and the resulting building stones at Broomfield look as if they came from a muddy foreshore in which the sedimentation rate was fast enough to limit the growth of the oysters sometimes seen on concretions in churches.

A more direct method of working on the provenance of the bored concretions is to record the colours of the pre-collection weathering zones by direct comparison with the Geological Society of America Rock-Color chart held up in the same illumination. Holes cut in a grey cardboard (N7) are placed in front of each spot on the stones. Weathering in the wall mainly has the effect of exfoliating the outer layers and increasing the lightness value. Probably this weathering was limited by a covering of limewash mortar until the Victorian era. The stones display bright colours developed in Pleistocene subsoils and later to greys modified in deoxygenated foreshore muds.

Much time at Broomfield was spent on measuring 70 individual coloured areas on typical concretions at the S.W. corner of the nave another 47 in and directly around the bored concretions. Using the conventions of the Munsell Color Company these two sets of observations have slightly different averages equal to 0.42 Y 6.314/3.286 in the S.W. corner and to 9.57 YR 6.149/2.660 in the unusual area including borings. In the rough terminology of American words the typical Broomfield concretions average as a dusky yellow and the abnormal area of the wall with borings as pale yellowish brown. At the times I noticed that one set of Plydora borings were in a greyish orange (10YR 7/4) surface, around an unusually dark core of moderate brown (5YR 4/4) which also formed a hard cortex to an adjacent unbored ellipsoidal concretion with a soft pale orange interior (10 YR 8/6). The adjacent fragment with the bivalves in it showed a similar pale orange exterior (10 YR 7/4) which had exfoliated in the 5 mm thick cortex of the Polydora borings to show the more original colour to be greyish orange pink (5 YR 7/2). Previous experience suggests that this layer was once composed of hydrogen sulphide developed in foreshore muds and around empty Ploydora borings, and has presumably become lighter by oxidation in the dry wall. Inside this cortex the bivalve concretion had a very pale orange (10 YR 8/2) exfoliated matrix. Elsewhere in the wall darker brown matrix and locally red stained joints seen in the abnormal area were less conspicuous and this is reflected in the average colourations subsequently calculated.

Broomfield Church, Essex (Part 1)

2006-11-11T14:12:00.000-05:00

November 3 2006. The parish church of Broomfield, originally dedicted to St. Leonard and now to St. Mary the Virgin, lies on the ancient route from Bury St. Edmunds, via Braintree and Ingatestone, to Roman London. The parish resembles Prittlewell and Sutton Hoo in evidently being an early Anglo-Saxon administrative center, with archaeological evidence of prosperous graves situated away from the church, which was presumably avoided in the Pagan era. But perhaps the burial of people around churches is a modern custom developed when the church took over administrative functions and in other parishes, such as Ingatestone, the site of the moot and gathered tithes? I visited Broomfield today to see whether it resembled Ingatestone and Braintree Churches in showing a large stone of Saxon-era significance along the road, and to study the Eocene London Clay concretions present in the walls of many older Eastern Essex churches and castles. According to the Inventory of the Historical Monuments of Essex, volume 2, by the Royal Commission of Historical Monuments they are erroneously described as “lumps of brown boulder clay” embedded in most parts of the church with “flints and short courses of Roman Brick.” The historical dating in their account is doubtless more correct and shows that the round early 12th Century west Tower lacking the London Clay concretions was added to their concentration in the south wall of the Nave and western Chancel built in the 11th Century (i.e. perhaps Saxon or earlier Norman). The Tower was presumably built with the similar one at Great Leighs, 6 km to the N.E. and off the old road, by visiting builders who employed the superior building stone of flints for their work, and perhaps brought it with them to both sites. However when the church was enlarged to the east and north in the 15th Century and modern period the London Clay concretions were used again, and this was also the case in the “modern” South Porch of the Royal Commissioners. One can easily imagine parts of the old wall being removed to make extensions and then that stone being used again partly to save transport costs and partly to match the colour and texture of the existing exterior. However, the part of the northern walls added since the Commissioners Report, which we would term new if modern is defined as post-1714, has much the same appearance without including any London Clay or Roman materials in it.

I intend to add a technical account of the colour and fossil content of these particular London Clay concretions in the Nave as a later entry to the blog. The typical material was studied on the west side of the porch among Roman Bricks or tiles. One of the Roman bricks was easily measured on the S.W. corner quoin there as having square dimensions of 290 mm by 290 mm, with a variable thickness of 35 to 45 mm, and having a no interior black reduction band on display. These were, however, seen in smaller fragments of probable Roman tile in the main part of the Nave walls. Flints with a white patina and various rather scarce sandstones were also present, but it is London Clay concretions that dominate and is the “stone that is weathered a strong mustard yellow” in the description by Norman Scarfe (A Shell Guide to Essex, Fuber and Fuber, London). Probably these concretions and the Roman Bricks are derived from an earlier Saxon structure on the site, which may have been built along the route when St. Edmunds boy transported to London or in the remote period of the Saxon gravegoods. Prittlewell Church certainly existed, and was modified, around the time of the early 7th Century burials, without them being shifted towards it. What I did notice was that a large stone was indeed present as expected in the Nave wall at Broomfield, and projecting about 400 mm south from it. It consists of 90 mm long, white and other irregular flints cemented by hard ferricrete or perhaps even silica, into a Puddingstone (sensu Royal Commission, but not the Hertfordshire Puddingstone of geologist’s). The resulting boulder has a diameter of 0.4 m and a length of at least twice that extending to secure it in the Nave wall just west of the 14th Century S.E. Nave window. Perhaps it had functions at that time as a table for alms given to the poor, or as a mounting block for horse riders on a lower ground level? The various studied descriptions of the Church do not note it at all. However, originally it may have been where tithes and manorial obligations were made in a moot operating in the northern half of Chelmsford Hundred, in a similar way to the Kings Hill gathering at Rayleigh and at the Ingatestone.

Winter arrives in Southend.

2006-11-10T13:57:00.000-05:00

November 2 2006. Media reports from a lightship in the southern North Sea at 4 Hrs. G.M.T. indicate that the drop in the temperature of my experimental seawater tank was able to cause sinkings due to a rise in barometric pressure after variable pressure in a gale. On the morning of October 31 the temperature was still 58½°F (14.7°C) and the pressure of 100.8 KPa was associated with a SW by S wind of force 7. Next morning the temperature had dropped to 52½°F (11.4°C), the pressure was 102.0 KPa and the cold wind was force 6 from the northwest. This morning the wind had moderated here but was reported offshore as force 5 from the N.N.W. at a pressure of 103.1 KPa. The tank water temperature had declined further to 48°F (8.9°C) causing the 8th of a set of 10 dry fallen Pinus pineaster Aiton cones to sink apex-up in the night, after about 113.0 days (length 104 mm, diameter 37 mm). Most of the sinkings due to the sudden arrival of winter took place on November 1st. During the first cold night a brown decayed 66 mm diameter apple sank in freshwater after about 21.5 days and was moved to seawater to see how much longer it would float in denser water with salt ions presumably diffusing into largely flooded, brown decayed flesh. The cork present in a bucket of seawater sank after about 2056.7 days, with the surface originally punctured by the corkscrew predictably at the base. The angle of tilt of this cylinder (46 mm by 23 mm) was 45 degrees. At 15 Hrs. the ash log in the same recently illustrated apple bucket sank horizontally after 31.0 days. It had more elongated dimensions (200 mm by 60 mm). At around 17 Hrs. a probable curlew secondary wing feather sank entirely intact and vertical after 58.2 days (length 119 mm by 18 mm vane width and 2.6 mm maximum calamus diameter). Of these only the cork qualifies as a long-term floatation defining seasonal singularities in sinkings reviewed from 37 cases in The Drifting Seed vol. 12 (no.1), p9-10. Since that report a charcoal sank on July 16 after 1548 days at 17.8°C and 102.6 KPa and now the cork as noted above. Usually the annual cooling event is from November 14 to 19, but there was one previous sinking at this time of year in my data set. This was a pumice stone sunk by 7 Hrs. G.M.T. on November 2 2001 at a higher temperature (13.9°C) and pressure (104.0 KPa).

These events took place during a period of low actual and predicted high tides at Westcliff to Chalkwell beaches. The morning strandline of October 31 was predicted to be 1.8 m above mean sea level at 5.27 Hrs. and was briefly studied at Westcliff around 13 Hrs. The strandline had by then been modified by sand blowing along it from the west but was still well defined by strings of Fucus, Zostera and reed tops bound into spiral bunches. Whiteweed (Serturlia) was present from the lower intertidal zone exposed to the gales. Paired Mytilus and Cerastoderma shells had stranded. A few green Halimone leaves were also observed. They would have been able to remain floating since the tides reached their higher level on the intertidal zone around October 25.

Many Halimone leaves were deposited with Fucus, twigs, gull feather and seawater on the Westcliff promenade by the O.44 Hr. G.M.T. tide of October 23. The predicted height of this tide was 2.7 m above mean sea-level but the debris was much higher than that and the waves probably removed the Halimone leaves from insitu plants at that time. It also rained later that day and not much since then, so that the buoyant yellow-red apple stranded with a few leaves on October 31 had probably also been in the sea for a week. This stranded apple was damaged on one side, probably by falling from the tree rather than by stranding on weed and sand. It was collected and refloated in seawater on the beach and has remained floating in the tanks, stalk-up since then.

The visit to Chalkwell beach after the similarly low morning tide of November 1st showed that a live Brent Goose had returned from Siberia and was swimming in a tide that was only slowly retreating from a poorly defined strandline. Presumably the north wind had prevented Fucus and other buoyant materials from stranding on the south-facing beach. Even the algal concentrations on the west side of breakwaters may have arrived earlier with the westerly gales and similarly low high tides. However, the new patches of gravel near the top of the wet part of the beach sand were associated with a few gull and oyster catcher feathers, which had stranded recently.

On land the birds now seem to go about in one flock; including one Wren, Blue Tits, a pair of Blackbirds, House Sparrows and even an aggressive Robin. Perhaps the gardens are normally now so full of parking lots and decking that the birds need to protect each other from cats and hawks by moving together from one exposed bird table to the next? Before the cold wind, and as recently as October 27th (and again on Nov 9th) there were more solitary visits from the attractive large Red Admiral Butterfly Vanessa atalanta. At 9 Hrs. G.M.T. on October 25 a bold large fox nearly walked into me in the urban setting of Lansdowne avenue Chalkwell, near the busy A13 road. It decided it would retreat behind a parked car before going on over the street, which was not displaying any garbage, bags that day. As far as the leaf fall is concerned, one ash tree has now (November 2) lost all of them while the one next to it resembles the local Hawthorne and oak in still having an insitu and largely green leaf displays. Frogs still sing in the day and hedgehogs still scream in the night last week.

Floatation of Tilia leaves in seawater

2006-11-09T14:13:00.000-05:00

October 25 2006. According to various botanical books the structure of a deciduous large leaf consists of a waxy epitheluim which keeps gases out except via pores (stomata) on the lower paler green surface. These stomata close to prevent water from moving through them, and are adjacent to a lower layer of cells between an air cavity space termed the spongy mesophyll. The upper half of the leaf also contains some air between more continuous palisade cells, and had a darker brown colour between the supporting veins on a yellow fallen Tilia which sank first. All of them looked more transparent and yellow near the black veins and more brown and opaque on the upper surface between the veins when later dried-out. But it is still rather unclear why some of these yellow fallen leaves sank quicker than in those in the green parent condition and the others much longer despite being more damaged. Probably the larger air spaces contract and the replacement of the water held inside the palisade cells by more salty water that prevents or slows their decay to producing brown opaque bacterial/fungal material. Certainly the experimentally sunk leaves did not look more altered. It must therefore be presumed that the uniform brown colouration of stranded leaves seen today (Oak and various others not Tilia) developed on land, or during drying on mudflats etc..

Tilia leaf

The example of a test of leaves was started on October 17 with the collection of 10 yellow fallen and 10 picked green Tilia leaves at Braintree (west of the southern end of New Street and fallen on to a parking lot). After five hours in a plastic bag they were floated in all the recently illustrated buckets and tanks of seawater. A brown set collected on January 30 2001 was dried between newspapers before being similarly tested 26 days later.

The sinking of these leaves in buckets and tanks did not appear to depend on water quality. It involved estimation of times when they sink in the night, or between observations. My method has been to stay up for the first and last sinkings of a set, if sinking looked eminent, and not worry too much if the sinkings around the average had to be roughly estimated. Usually I have studied undried leaves so I was not satisfied with the seven previous Tilia times from dried brown and decayed material. The results for the tree sets are as follows (latest at 15°C):

Brown (7) Av. 6.67 days (range 0.847-10.124)

Yellow (10) Av. 2.1165 days (range 0.811-6.679)

Green (10) Av. 2.178 days (range 1.654-2.694)

The average dimensions of the green set were 85.9 mm by 78.5 mm width on the leaf itself, and 126.8 mm inclusive of the peteole or stem. The largest actually sank fist and had corresponding dimension of 128 mm by 123 mm, and 175 mm total length. The yellow set provides a more natural sampling of the leaf fall and averaged 67.0 mm by 61.8 mm width, with a total length of 96.0 mm. The largest leaf was the last to sink, probably because the peteole was shorter than the penultimate sinking of one with the same overall length of 130 to 131 mm in 3.047 days. These two yellow leaves respectively measured 80 by 68 mm width and 93 by 74 mm width on the leaf itself. Where the leaf was longer on the sides than along the central vein I measured the later, and where damage to the tip had occurred I estimated this length. The damaged leaves actually had averaged times and were relatively small, but the two longer floating yellow leaves did look thinner and paler on the upper surface when finally dried-out.

Incidentally, I am not sure which species this downtown Braintree belongs too. Judging from the larger leaf size, it would be Tilia platyphyllos Scopoli; but the hairs on the lower side of the leaf were confined to vein branches as in the hybrid between it and the Nature north Essex Tilia cordata Miller, termed Common Lime or Tilia x europaea L. In Germany the genus in termed Linden and in eastern North America Basswood. But Linnaeus, probably following the Braintree/Notley resident John Ray, correctly identified it with Tilia of Virgil and Ovid. Presumably the downtown Braintree tree is not old or Native enough for Ray to have studied it himself.

Tilia platyphyllos

Drifted L.E.C.A.

2006-11-02T15:20:00.000-05:00

October 14 2006. The Light-weight Expanded Clay Aggregates (L.E.C.A.) found stranded on Chalkwell Beach on October 9 and sampled coming in with the tide at Westcliff the next day correspond to a sentence by G.C. Cadée in his article on Texel beaches in The Drifting Seed vol. 11 no. 2 p.5 (Sept. 2005) namely “building stones of this expanded clay are made and those much larger stones one can find also in drift on our beaches.” His report was mainly about 7 mm spheres found there, with yellowish surfaces around dark purple coloured shallow cracks. both were made by calcination of the middle London Clay Formation at 1200°C in the LECA (G.B.) pits and factory at Mill Lane, High Ongar, Essex c. 1968-1995. However they are potentially made from various clay sites around the world and I have assumed that the Ongar pits ran out of clay, at least from there. On taking both the drifted material and part of one currently being used on a building site to a builders merchant, I was informed that they are marketed as CELLON BLOCKS but not where they are currently made. They doubtless get put into the sea either by illegal flytippers, or as part of official dumping of hardcore to improve sea defenses, and then float away!! I had not noticed them before and initially assumed that Lower Greensand Cretaceous sandstone pebbles in the recently repaired seawall had already come loose. They might also be confused with concrete until picked-up and the following description is made here for beachcombers and geologists.

As seen on building sites the blocks are rectangular with a length around one foot or 30 cm (I am not sure exactly which; doubtless 30cm in the Netherlands) with easily broken edges showing a pitted, rather than actually porous, rough interior. Two colours were seen both on the beach and on house building sites at Southend-on-Sea this week. A dry inland fragment (110 by 85 by 60 mm) was light bluish grey (5B 6/1), changing on both the submerged and the emerged surfaces to dark bluish grey (5B 3/1) after about five hours in an oxygenated seawater tank. The other type is very light grey (N8) and represented by the sample taken from the sea (180 by 130 by 60 mm worn subtriangle) given a light greenish grey (5G 8/1) colour by a thin film of algae and having dark yellowish grey colour (5Y 7/1) on the less easily coated original surface of the block. The latter look very much like clay which has been cut and smeared by a spade or mechanical digger, while the rough surface of both colour varieties consists of rather square 0.5 to 0.8 mm wide pits, between thin walls of silty vitrified clay showing a few dark spots of what was once presumably pyrite. Perhaps the blue variety is a more originally pyritic clay, or more likely one processed in a more reducing environment. One of the yellowish blocks from the beach was placed in the deoxygenated seawater bucket for two days and seen to go uniformly dark bluish grey below the waterline. This stain differs from the hydrogen sulphide staining of the wood, bone and aragonite shells on Chalkwell foreshore in being entirely lost again when exposed to dry air overnight. Both varieties have 10 to 20% of the volume above the waterline and do not appear to be sinking like pumice initially does.