FOSSIL MOLLUSC A. 285 



in a state of high perfection, the bivalve shells im- 

 bedded in it being frequently found double. At Ged- 

 grave, Gomer, and the neighbourhood, by digging a 

 few feet we come upon the original and undisturbed 

 Coralline Crag, very rich in molluscan remains. As 

 we ascend from the lower areas where this bed occurs, 

 and come to the higher grounds, we reach the out-crop 

 of the second or rocky Coralline Crag. Many pits are 

 exposed in it in the neighbourhood of Orford and 

 Sudbourne. For obtaining fossils, the Aldborough 

 section is perhaps better than those of the same beds 

 at Orford. Mr. Searles Wood, sen., considered that 

 nothing among the fossil shells yet obtained from the 

 Coralline Crag indicated the latter to have been formed 

 under a greater depth of water than from thirty to 

 forty fathoms. 



Professor Prestwich thinks that after the Coralline 

 Crag sea had attained its greatest depth, a change took 

 place, and a bed of comminuted shells was spread over 

 the deep-sea bed. Further elevation exposed the sea- 

 bed to the action of tides and currents, to the denuda- 

 tion of the lower beds, and heaping up the Bryozoa 

 and MoUusca of the later deposits in banks. The 

 water continued to get shallower, until a continuance 

 of the elevatory movement gradually raised the Coral- 

 line Crag above the sea, where it was exposed to the 

 considerable denuding action which removed so large 

 a portion of it. During the Red Crag period im- 

 mediately succeeding, the Coralline Crag was broken 



