FOSSIL MOLLUSC A. 287 



thus supplied. Thus he regarded 159 species as ex- 

 tinct, the recent forms numbering 168, or a percentage 

 of rather more than half. Of these he considered 139 

 species to be still living in British seas, whilst twenty- 

 seven species were confined to southern, and two to 

 northern seas. 



The Red Crag is formed of a succession of beds, 

 varying from two and three to nearly twenty feet in 

 thickness. The layers are composed of sand and 

 shells, and many sections show them inclined at a 

 considerably high angle. This structure is altogether 

 different from that known as " false bedding," although 

 the latter occurs to a considerable extent in the Red 

 Crag. In Bawdsey Cliff, and also in the cliff at 

 Felixstowe, this oblique lamination is very distinctly 

 shown. Geologists regard this phenomenon as the 

 accumulations of a foreshore. At Sutton the Red Crag 

 is bedded or banked up against an older Coralline 

 Crag cliff. Mr. Wood regarded the Red Crag 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 re-accumulated ; 

 every bed representing some of this destruction and 

 re-accumulation, 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 accumulated those 



