PRESTWICH CRAG-BEDS OF SUFFOLK AND NORFOLK. 



333 



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 divi- 

 sion of the Eed Crag in the typical Sutton district, before com- 

 mencing with the district further north. 



The upper division of the Eed Crag I have formerly designated, 

 o-wdng to the want of all fossils in the neighbourhood of Ipswich, 

 as the "unproductive sands" of the Eed 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 Eed 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 immedi- 

 diately preceding the deposition of the upper bed*. There is great 

 difficulty (in many cases amounting almost to impossibility) in show- 

 ing 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 

 Eeculvers, where it seems to pass gradually down into the Thanet 

 Sands. Therefore the apparent passage of two soft beds is unim- 

 portant when elsewhere a decided line of separation can be shown to 

 exist. Where the upper division of the Eed Crag reposes quietly 

 upon the lower one, the similarity of Uthological 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 f. 



Some appearance of this upper division may be seen in the cliff at 



r ^~ — ijj _ r t it] nj w n 



tJ Yaze. 



a. Gravel. 3. Grey clay. 3'. Light coloured -md 



2. Crag beds. I. 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." 



t The line of division often shows best under certain conditions of weathering 

 and moisture. 



