352 PEOCEEBINGS OP THE GEOLOGICAL SOCIEIT. 



the great majority, viz. 150 species, are still found living in British 

 seas ; whilst of the 55 species not found living in British seas 32 are 

 now restricted to more southern, and 23 to more northern seas — 

 showing, with respect to the Coralline Crag, a gain of 9 northern, 

 and a loss of 33 southern species. 



The total number of species common to the Red Crag and 



to the Coralline Crag is 186 



Or, deducting extraneous species 46 



140 



This gives a percentage of species common to the Bed and Coralline 

 Crags of about 62. Or, looking at the percentage of living species 

 in each, the difference between them is much less, taking even the 

 smaller percentage due to the exclusion of the extraneous species. 



In the Coralline Crag 84 1 , j? ,• • 



In the Bed Crag . . 92 | P^" «'^^- '^^ ^^^S species. 



CON-OLTTSION. 



In the former part of this paper, I remarked that the Coralline 

 Crag had, during its latter stages, been subject to a process of slow 

 elevation, but probably without rising above the sea-level. It had, 

 however, emerged above the sea at the commencement of the Bed- 

 Crag period, as evinced by the shore-line at the base of the Bed Crag 

 at Sutton (see Bl. VL), when the Coralline-Crag reef or islet stood 

 some 40 feet or more above that shore-line. The difference of level 

 between the lower shore-line and the surface of the London Clay 

 under the Bed Crag in the adjacent district is not more than a few 

 feet, whence the Bed Crag must have been accumulated in a shal- 

 low sea. Mr, Searles Wood, Jun., considers that the lower division 

 of the Bed Crag is arranged in successive beach-stages. There seems 

 to me, on the contrary, to be an absence of definite order; and the la- 

 mination and bedding which he considers referable to beach-action, I 

 think may in all cases be referred to the variable bedding and oblique 

 lamination produced by the shifting of shoals and sand-banks at the 

 bottom of the Bed-Crag sea, as was the case with the upper division of 

 the Coralline Crag {ante, fig. 3, p. 120). Mr. Wood, Sen., has already 

 expressed his opinion that the peculiar stratification of the Bed Crag 

 must be owing to the constant shifting of the sands and shingle 

 caused by variable and changing currents ; and this is also the opinion 

 of Mr. Jeffreys. Shoals may have been formed and removed in 

 part or wholly by a change of currents, just as now is of constant 

 occurrence off the present Suffolk coast. 



This sea was not only shallow, but was studded with reefs of Coral- 

 line Crag, amongst which strong and shifting currents set in ; whilst 

 in winter the more distant Chalk and Tertiary shores were fringed 

 with ice, which, as it floated off, carried away large, massive flints, 

 and deposited them in the Bed Crag (fig. 21). In the same way ice- 

 borne blocks and fragments of the Coralline Crag were carried from the 



