Page:Quarterly Journal of the Geological Society of London, vol. 27.djvu/494

 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 Red 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

In the Red Crag 92    per cent. of living species.

Conclusion.

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 Red- Crag period, as evinced by the shore-line at the base of the Bed Crag at Sutton (see Pl. VI.), 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 Red Crag in the adjacent district is not more than a few feet, whence the Bed Crag must have been accumulated in a shallow sea. Mr. Searles Wood, Jun., considers that the lower division of the Red Crag is arranged in successive beach-stages. There seems to me, on the contrary, to be an absence of definite order; and the lamination 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 Red-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 Red 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 Coralline 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 Red Crag (fig. 21). In the same way ice-borne blocks and fragments of the Coralline Crag were carried from the