vi SUPPLEMENT TO THE CRAG MOLLUSCA. 



feature. The pebble heaps of the London Clay basement bed about Bickley, in 

 Kent, not unfrequently exhibit this, while the Lower Glacial pebble beds (to 

 be spoken of hereafter) in the neighbourhood of Halesworth and Henham exhibit it yet 

 more distinctly ; their oblique bedding, which is constant and parallel throughout sections 

 between twenty and thirty feet in depth, contrasting with the horizontal bedding of 

 equally deep sections of the same pebbles at other localities — the one case representing 

 the accumulations of a foreshore subaerially heaped up under the action of tide and surge, 

 and the other the same accumulations spread out under a shallow sea. This beach or 

 foreshore character pertains to a large part of the Red Crag, and well agrees with some 

 of its other features ; as, e.g., the intercalation occasionally of land and fresh-water shells in 

 a truly marine deposit, which presents none of those intermediate features that occur in a 

 fluvio-marine one •} the presence of beds of Cardium double, as they lived among the tossed- 

 about heaps of other shells ; and the bedding up of the deposit against and around a low 

 cliff of Coralline Crag (as at Sutton) which is perforated by lithodomous mollusca. The 

 Red Crag thus presents itself as the remains of an extensive series of banks that were 

 more or less dry at every tide, and that were from time to time partially swept away and 

 reaccumulated ; every bed (of which three or four are often to be seen resting on one 

 another) representing some of this destruction and reaccumulation, since the top of every 

 preceding bed is planed off evenly to form a floor for the next above, in the base of which 

 small pebbles and small rolled phosphatic nodules often abound, in some cases forming thin 

 bands. In the channels which permeated these banks there seems to have been accumu- 

 lated those portions of the Red Crag which exhibit the true features, often very extreme, 

 of false bedding. If we examine any long section of this beached-up Crag where its 

 base is exposed, such as in the cliff at Bawdsey, we do not find beneath it that 

 bed, several inches thick, of phosphatic nodules which occurs in the various pits worked 

 for nodule extraction, nor any of those large angular flints and masses of Septaria so 

 abundant at the base of the Crag, where it is thus worked ; while in these pits we find an 

 absence (at least in the beds immediately over the nodule bed) of those foreshore features 

 just described, and in their stead true and often very fantastic false bedding. An 

 inference seems to follow from this that where these flint erratics and Septaria masses 

 occur we have the bottoms of the channels permeating the banks, up which there drove 

 floating ice freighted with flints from some chalk shore ; and that these channels afterwards 

 silted up and became part of the banks, for it is very remarkable that none of these 

 erratics occur in the body of the Crag itself. If the main mass of the Crag had been 

 deposited under water, we should naturally expect to find the large flints and masses of 

 Septaria, so abundantly present in places at its base, distributed through the entire mass of 

 the formation. 



1 Mr. Bell, in vol. viii of the ' Geol. Mag.,' p. 451, gives a section at Butley, where a bed of land and 

 fresh-water shells is intercalated between two of these beached-up beds of Red Crag. 



