354 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



or exposed during certain states of the tides till the surface became' 

 dried and fissured so as to form wedge-shaped cavities filled with the 

 materials of the beds which were accumulated above them (fig. 8). 

 In beds deposited under such circumstances, subject to such constant 

 removal and reconstruction, it is not surprising that it is difficult 

 to find one in which the shells of the period exist in situ. Possibly 

 some of the beds at Walton were less frequently disturbed, or may 

 have been deposited under rather more tranquil circumstances than 

 elsewhere ; still most of those beds are full of comminuted shells, 

 and many of them show oblique lamination, so that they also were 

 subject to the action of tides and currents. "With a sea of this 

 character, and with shoals and reefs of the soft friable Coralline 

 Crag exposed to its action, a large destruction of the latter was in- 

 evitable ; and the shells of that deposit must consequently have been 

 transferred in great numbers to the newer beds of the E,ed Crag 

 formed around it. To what extent this may have taken place it is 

 not possible yet to say. I quite agree with Mr. Searles Wood, that 

 a large number of the shells found in the Red Crag have had this 

 origin ; but althoxigh we can feel little doubt on the subject, yet as 

 the shells are mostly single valves, and the staining given by the 

 Red Crag assimilates them to its own fossils, it is dilficult to di- 

 stinguish those which are derived from those which belong to the 

 deposit. When we meet "with the entire or the rolled fragments 

 of Bryozoa or some of the rare corals, evidently derived from the 

 Coralline-Crag beds, there can be no doubt of their origin. Still 

 it is clear that a considerable number of shells lived in the Red- 

 Crag sea, and that a certain number of new species were introduced. 

 Many species of bivalves are found double ; but this is not always a 

 proof that they are not extraneous, 



I believe also that a large proportion, if not all the coprolites 

 (so called) of the Red Crag were derived from the Coralline Crag, 

 as detached ones are found not unfrequently in its mass, and a bed 

 of them was found to underlie it at Sutton, at the only place where 

 its base has been exposed (ante, p. 117). 



The direction of the currents, judging from the nature of the 

 foreign materials found in the Red Crag, seems to have been from 

 the east to south-east. Though the sea was open to the north, the 

 communication with the south was probably cut ofi'. Innumerable 

 Bcdani covered the blocks of Septaria and flint scattered on the 

 London Clay and Chalk-shores of this Red-Crag sea. Pholades 

 abounded on its water-line ; and we have seen at Sutton and else- 

 where that Mytili were common in its shallow waters, while other 

 genera found shelter in bays and any tranquil places. I can see no 

 distinction in the organic remains, from the base of the Red Crag to 

 the top of the lower division. The like abundance of species of 

 Pectuncidus, Mactra, Tellina, Cardium, Fusus, Natica, Purpura, &c. 

 occurs almost throughout, modified by situation, and having a distribu- 

 tion sufficiently independent in character to show that it could scarcely 

 have been dependent upon one source alone, and that a derivative 

 one, for its fossils, but that there were banks and feeding-grounds 

 for the various species of Mollusca, which served as centres from 



