Rock colours at Prittlewell Priory

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

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

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.