J. A. Birds — Geology of the Channel Islands. 79 



The deposits referred to occur now as little patches within the area 

 bounded by the great terminal moraines. 



As physicists themselves are not yet quite agreed upon the 

 subject of glacier-motion, it is not incumbent upon the geologist to 

 explain the precise mode in which a thick mass of ice can creep 

 over the surface of incoherent beds without entirely demolishing 

 them. It is enough for him to show how the remarkable distri- 

 bution of the interglacial beds, and the various phenomena presented 

 by these deposits, indicates that ice has overflowed them. It is 

 useless, therefore, to tell him that the thing is impossible. The 

 statement has been made more than once that an ice-sheet several 

 thousand feet thick is a physical impossibility, but unfortunately for 

 this dictum the geological facts have demonstrated that such massive 

 ice-sheets have really existed, and there appears to be one even now 

 covering up the Antarctic Continent. We used also to be told, not 

 so many years ago, that the abysses of ocean must be void of life 

 for various reasons, amongst which one was that the pressure of the 

 water would be too gi'eat for any living thing to endui'e. Yet many 

 delicate organisms have been dredged up from depths at which the 

 pressure must certainly be no trifle. Now there seems to be just as 

 little difficulty in believing that these organisms existed in a perfect 

 state at the bottom of the ocean, as that shells imbedded in clay 

 would remain unbroken underneath the pressure of a superincum- 

 bent ice-sheet of equal or greater weight. If the ice were in motion, 

 the clay with its included shells might be ploughed out bodily, or 

 be merely crumpled and contorted ; or it might be ridden over with 

 little or no disturbance ; or, on the other hand, it might become in- 

 volved with subglacial debris, and be kneaded up and rolled 

 forward — the shells in this case being broken, crushed, and striated, 

 just as we find that the shells in certain areas of Till have been. 

 The fate of the fossiliferous beds would, in short, be determined by 

 the rate of flow and degree of pressure exerted by the superincum- 

 bent quasi-viscous body — the motion of which, would be largely 

 controlled by the physical features of the ground across which it 

 crept. 



V. — GrEOLOGY OF THE CHANNEL ISLANDS. 



By J. A. Birds, B.A. 



Fart L—The Older Bocks. 



IN the most extended view, the Channel Islands may be regarded 

 as fragments and relics of the Eastern or European coast of the 

 Atlantic, reckoning from the North. Cape to Cape St. Vincent, and 

 including the Western shores of Scotland and Ireland, and the pro- 

 montories of Pembrokeshire and Cornwall. They are excellent 

 illustrations, says Professor Ansted, " of those spurs and tongues of 

 porphyritic rock, of which almost all the promontories of the 

 Atlantic coast of Europe consist."^ Very small and insignificant 

 specks indeed they seem in such a length of coast, stretching from 



1 Tlie Cliaiinel Islands, by Ansted and Latham, 1862, p. 247. 



