The sands, silts and clays which overlie the raised beach at West Angle, and which lie beneath the reddish till, are so unusual that they have caused intense (and sometimes acrimonious!) debate among geomorphologists and geologists. Dixon (1921) referred to them as "loams" but that term is misleading since it is conventionally used for a sandy or silty soil, which implies a period of subaerial evolution beneath a plant cover. There is certainly some evidence (in the form of a peat bed) of vegetation accumulating and growing -- but it would be a mistake to simply assume that all of the sediments in this sequence were accumulating at the ground surface. They are very fine-grained, and many researchers have concluded that some of sediment accumulation was beneath water, either in a lacustrine, marshy or estuarine environment. So let's simply refer to this sequence of quite variable sediments as the "silt and clay series".
First, the base of the series. According to my observations, and those of David Unwin, there are ferruginous cross-bedded sands and gravels above the raised beach. These are generally less than 1 m thick, but Unwin interpreted them as "dune sands" and I am now inclined to agree with him. (I originally thought that they might be beach sands laid down on top of the pebble beach during the course of a marine transgression, but I now think that evidence in support of this hypothesis is in short supply.......) Another interesting fact is that stony grey silts up to 40 cms thick seem to be associated with these sands and with the upper part of the raised beach facies. This suggests that at the end of the raised beach episode (the Ipswichian interglacial?) sea-level might have dropped slightly, or else there was some other environmental change. This led to the accumulation of slope deposits or rockfall materials and pre-existing sediments on the valley side, with colluviation extending as much as 30 m from the valley side out onto the valley floor. Possibly a sand dune system developed on top of the raised beach with a dune slack behind it. Colluvial materials (incorporating angular rock fragments and also raised beach pebbles and shingle) were then interdigitated with sandy dune materials and with peats, silts and clays in a freshwater environment.
The Silt and Clay Series. Fragments of well-preserved oakwood, rootlets and leaves are found here and there, and Dixon (1921) referred to "plant fragments and occasional large pieces of wood." In "Nature" journal in 1968 I reported the conclusions of Dr Ian Simmons and other Durham colleagues regarding samples taken from the sandy and silty layers just above the raised beach. Ian showed that the pollen and plant remains are fully representative of an interglacial environment. Quercus (35% of total tree pollen), Alnus (43%) and Corylus (42%) were the dominant constituents, with Pinus only moderately represented (13% of tree pollen). Non-tree pollen accounted for 85 of the 343 pollen grains counted, with Gramineae, Cyperaceae and Filicales moderately well represented. Other lesser plant pollen (eg Chenopodiaceae and Armeria) suggesting proximity to littoral conditions. The vegetation was thus a mixed oak and alder forest with pine and hazel, with salt-tolerant plants close to the water's edge. Carex, Juncus and other water plants point to an environment that included small open pools with patches of marsh and fen and carr vegetation. Botanists who have examined my own evidence incline to the view that this was a fresh-water rather then a salt-water (estuarine) environment.
In 1973 Stevenson and Moore found the following sediment sequence:
Head deposits overlying:
Yellow/orange sandy silt
Grey/yellow sandy clay
Yellow/orange clay with abundant pebbles.
Apparently sharp hiatus
Stiff blue/grey clay with sandy bands at 106 cm. Organic sediments, laterally variable in nature were found within this unit, as was evidence of current bedding in the inorganic sediments.
Grey—brown silty clay. (with included Alnus wood layer). Organic remains become more abundant towards its base; especially obvious are wood fragments
Pebbles in a grey, sandy-clay matrix. Larger pebbles (up to 5 cm diameter) were concentrated in the lower layers.
Very fine white sand, cross-bedded
Very fine yellow sand with an iron-rich layer
Fine yellow and white sands, particles of larger size evident towards the base
Iron concreted, yellow and red sands
Coarse-grained yellow sands with hard bands of ferruginous, cemented material
Pebbly, raised beach deposits
One interesting feature of the work by Stevenson and Moore is the presence of a "hiatus" in the pollen sequence in their Zone WA-2. They suggest that there was an episode of extensive forest destruction, followed by secondary succession and woodland recovery, but resulting in a changed floristic composition. Such destruction could have resulted from flooding or erosion. The possibility of habitat disturbance as a result of factors associated with local fluviatile conditions is very real in this swamp-carr site. Marine incursion is also possible.
Another suggestion (and it is no more than that) is that towards the top of the sequence there is an increase in Pinus pollen and a decline in some other species -- possibly indicative of a "post-temperate" plant assemblage taking over from a truly interglacial one. Does this represent the end of the interglacial and the onset of colder -- and eventually periglacial -- conditions?