The next pit northward is that on Aldringham Common (known as the Thorpe Pit). As this, however, belongs to the so-called Norwich Crag, we will proceed first to describe the upper division of the Red Crag in the typical Sutton district, before commencing with the district further north.
The upper division of the Red Crag I have formerly designated, owing to the want of all fossils in the neighbourhood of Ipswich, as the "unproductive sands" of the Red Crag ; but this, although it holds good in the neighbourhood of Ipswich, cannot, if I am right in its correlation, be applied as a general rule. Mr. Searles Wood, jun., and Mr. Fisher, have also both noticed the presence of an upper and more horizontally bedded division of the Red Crag, and have remarked upon the difficulty at times of drawing a line of separation between this and the underlying beds, owing to the extent of erosion and denudation which had taken place immedidiately preceding the deposition of the upper bed*. There is great difficulty (in many cases amounting almost to impossibility) in showing where the line of separation really is placed. Where beds of soft sand or loam are superimposed one upon the other, whatever may be their difference of age, they must, when deposited under water, tend to intermingle at the point of junction, as I have shown in the case of the Loess in the neighbourhood of the Reculvers, where it seems to pass gradually down into the Thanet Sands. Therefore the apparent passage of two soft beds is unimportant when elsewhere a decided line of separation can be shown to exist. Where the upper division of the Red Crag reposes quietly upon the lower one, the similarity of lithological character and colour is such that the only cause for separating them seems to be the absence generally of organic remains in the upper division. But this is not a persistent feature, as there are places where this division contains shells, some of them of a marked character, to which we shall refer presently † .
Some appearance of this upper division may be seen in the cliff at
Fig. 12. — Upper 25 feet of the Cliff, Walton-on-the-Naze.
a. Gravel. 2. Crag beds. 3. Grey clay. 3'. Light coloured sand. l. London clay.
- I do not, however, interpret all the sections given by Mr. Wood (Ann. &
Mag. Nat. Hist. March 1864, pp. 3 & 4) in the same way that he does. I include in the upper division of the Crag some beds which he considers to belong to his " Lower Drift."
† The line of division often shows best under certain conditions of weathering and moisture.
