AUSTEN — TERTIARY DEPOSITS OF THE SUSSEX COAST. 59 



by which they were conveyed, — floating ice is not only a fully ade- 

 quate, but is perhaps the sole known agent which could have trans- 

 ported these masses ; and such I shall now assume it to have been 

 in this case. 



Thus much, then, has been established, that at a period indicated 

 by the clay-gravel-beds of the Sussex-levels, marginal shingle and 

 great blocks were drifted away from some coast-line composed of 

 crystalline and old palaeozoic strata, and which was neither that of 

 the West of England, nor yet of France (Cotentin). 



It may, perhaps, be objected to this latter exception, that, if we 

 admit of the supposition of climatal conditions favourable to the for- 

 mation of coast-ice, materials might have been floated away, not 

 only from the Cotentin and the Channel Islands, but also from much 

 greater distances along the French coasts, as from Brittany ; by in- 

 cluding which locality, the difficulty as to the points of origin of the 

 various materials at the present sea-level would be partly got rid of. 



The seemingly limited area over which the drifted materials are 

 distributed has an immediate bearing on the question as to what 

 was the distance and position of the place whence they were derived. 

 If we suppose that the Channel-area then stood in its present rela- 

 tions to the Atlantic, the nearest points from the Sussex-levels at 

 which coast-ice could pick up the various materials which have to be 

 accounted for, would be from 70 to 150 miles distant : once detached 

 from the coast, the floating masses would become obedient for many 

 days, at the very least, to the combined influence of the wind and 

 tide, before they were stranded, and would hence be distributed in- 

 difl'erently over a very wide area. The juxta-position of the larger 

 drifted blocks seems, therefore, to exclude this supposition, to point 

 at the same time to some nearer source, and to a somewhat diff'erent 

 agency of coast-ice. 



I have shown elsewhere that the western portion of the English 

 Channel area was occupied during several distinct geological periods 

 by a mass of crystalline and old palaeozoic rocks (Journ. Geol. Soc. 

 vol. xii. p. 45) ; that this mass gave way and subsided from time to 

 time, in a direction from west to east, by which process the present 

 area of depression was gradually formed. It will also be seen that 

 the eastern extension of this mass can be defined for several definite 

 geological periods. 



Apart from the older physical arrangements which form the sub- 

 ject of investigation in the memoir here referred to, it must have 

 been felt by most geologists that an eastern extension of the old axis 

 of the Channel-area is necessary to enable us to account for many 

 of the differences which present themselves in connexion with the 

 secondary and tertiary formations of France and England, so that 

 the supposition of a submerged mass of old rocks is by no means a 

 violent hypothesis, contrived to meet a special difficulty. 



This is not the place where such views as these can be enlarged 

 upon and illustrated. I may, however, be permitted to state, that 

 we have abundant proof that this old Channel-ridge existed and served 

 to define the form of the area in which the up})er fluvio-marme per- 



