114 J. A. Birds — Geology of the Channel Islands. 



years ago I ventured to describe, in this Magazine, a bed of chalk 

 flints near Spa, in Belgium,^ which I imagined might have been 

 deposited by floating-ice at the epoch in question. If this was 

 the case, and supposing the submergence to have been uniform and 

 general, it must have been to a depth of 1500 — 2000 ft., which 

 would have reduced all Europe north of the Alps and Pyrenees to a 

 sea, with only a few mountain or hill ranges — as the Harz, the 

 mountains of the Black Forest, the Vosges, the hills of Central 

 France, and some few summits in Brittany, remaining as islands in 

 the midst of the waters. 



This bed of chalk flints, therefore, I am unwilling to cite as evi- 

 dence of submergence ; although it is not necessary to assume that 

 the depression was either uniform or general. 



But to return to the question of the clays, etc., and flints of the 

 Channel Islands, and the probable origin of their presence there. 



Only two or three causes, it is evident, are probable or possible. 

 Either (1) they are the relics — and meagre ones indeed — of a former 

 extension of the Chalk or some later formation containing flint- 

 gravel upon or near the spot ; or (2) they must have been trans- 

 ported from a distance, and that either by oceanic currents, or by 

 ice : and of these two alternatives the latter is surely far the more 

 probable. 



It is not necessary indeed, as was said above, to suppose that the 

 South of England was submerged so as to allow of the passage of 

 ice-rafts in a direct line from the north ; these might still have 

 wandered up and down the Channel from the S.W. or N.E., 

 occasionally bringing freights of chalk and flints with them. That 

 such ice-ships were wafted, even from the south, has long since 

 been inferred from the presence of erratic blocks on the coast 

 around Selsea Bill and Pagham, which are believed to have come 

 from Brittany or the Channel Islands. These blocks, indeed, are 

 adduced as evidence of an ancient coast-line existing there during 

 the intracontinental period — and therefore of the non-submergence 

 of the South of England. No one, however, can say how far such 

 a coast-line might have extended east and west ; and, therefore, it is 

 scarcely an argument against a general submergence of the country 

 south of the Thames and the Bristol Channel such as I have been 

 advocating — in which case, it is obvious that the amount of chalk 

 and flints borne southwards, e.g. over Salisbury Plain, and between 

 it and the Mendips. would be very greatly increased. Also, if the 

 submergence extended to the Channel Islands, it would account for 

 the clays, etc., containing flints (on the summit of Guernsey), which 

 would not be accounted for otherwise. 



The evidences of elevation of the British Isles during the first and 

 second continental periods, and of submergence in the intermediate 

 time, are clear and numerous, as regards the country north of the 

 estuary of the Thames and the Bristol Channel ; and as yet they 

 are, and perhaps always will be, few and obscure to the south of 

 that line ; but is it reasonable to suppose such enormous movements 

 1 Geol. Mag. 1866, Vol. III. p. 501. 



