728 ME. F. W. HAEMER ON THE CEAG OF ESSEX. [Nov. I9OO, 



V. The probable Conditions under which the Red Crao 

 Deposits originated. 



The Coralline Crag deposits are of two kinds : first, the shelly 

 sands, principally organic, the subject of my former paper, origin- 

 ating as submarine banks in water of a moderate depth ; and 

 next, coarse rolled material, containing mammalian and other deri- 

 vative fossils, the littoral drift of that period, accumulated as the 

 basement-bed of the formation, at a time when strong currents 

 from the south or south-west were entering the Crag basin, and the 

 beach was consequently travelling from south to north. 1 The latter 

 deposits, known in situ at Sutton only, where they occur at the base 

 of the Coralline Crag, represent the earliest invasion of East Anglia 

 by the Pliocene Sea. As submergence proceeded, and these base- 

 ment-beds were covered in places by shelly sands, the shore-line 

 was carried somewhat to the west, where accumulation of littoral 

 debris still went on, contemporaneously with that of the former, 

 farther from the coast. 



At the close of the Gedgravian (Coralline Crag) Period, an up- 

 heaval of the southern part of the Crag area took place, causing 

 some denudation, apparently greatest towards the south, as the out- 

 liers of Coralline Crag in that direction, at Tattingstone, Eamsholt, 

 and Sutton, are small and probably fragmentary. This denudation 

 destroyed any of the shelly sands (with the exception of these 

 outliers) that may have existed in that part of the Crag district ; 

 but the boxstones and other debris associated with them, better able 

 to stand the wear-and-tear of the advancing sea, were preserved, 

 and went to form the basement-bed of the succeeding Red Crag." 

 That the sources from which they were obtained were cut off before 

 the Red Crag Period (possibly by the southern elevation which 

 destroyed the communication between the North Sea and the 

 English Channel, and interrupted the tidal currents from the south 

 till then existing) is shown by the fact that no such littoral material 

 is found in the lied Crag, except towards the base of the formation. 

 If we adopt the view that the mammalian remains contained in 

 these basement-beds, equally with the mollusca of the boxstones 

 with which in Suffolk they are found, are derivative, 3 that they 

 were brought into the Crag area by currents, or by the travel of the 

 beach, at the commencement of the Gedgravian Period, having been 

 derived principally from Pliocene strata older than the Coralline Crag 

 formerly existing to the south, 4 and that the nodule-beds originally 



or from the Newbournian to the Butleyan district. The subject is perhaps one 

 upon which there is room for a difference in opinion ; on the whole, however, 

 I believe that the lists of shells from the various Eed Crag localities correctly 

 repi'esent the rnollusean fauna of each zone. 



1 Quart. Journ. Geol. Soc. vol. liv (1898) p. 315. 



2 See also H. B. Woodward, « Geol. Engl. & Wales' (1876) p. 285. 



3 We could hardly expect them to occur so abundantly in a marine deposit, 

 if they were not derivative : the remains of land-mammalia are not usually 

 found under such conditions. 



4 Mr. P. F. Kendall and I found in September 1899, on the beach at Folke- 

 stone, fragments of indurated ferruginous sandstone, of composition similar to 

 that of the boxstones, which had fallen down from beds of Lenham (Diestian) 

 age at the summit of the cliff. 



