﻿Date of the Glacial and the Upper Miocene Period. 207 



years, we may be quite sure that by means of sinkings of land 

 many such striated rocks have become sea-bottom; the conse- 

 quences of which would be that the glaciers would have melted, 

 and the stratified rocks would retain their striations, which would 

 be well protected by the thousands of feet of sea-water they 

 might have above them. Their moraines of erratic blocks would 

 be sure to be deposited at the sea-bottom also. And the ground 

 may have risen again since, and even in some cases risen and 

 sunk again and again. Denudation would, I fully agree, oblite- 

 rate all striations which were exposed to it long enough in sub- 

 aerial situations. Again : — 



" But do icebergs striate the rocky bed of the ocean ? Are they 

 adapted for such work ? It seems to be almost universally as- 

 sumed that they are. But I have been totally unable to find any 

 rational grounds for such a belief. Clean ice can have but little 

 or no erosive power, and never could scratch a rock" (p. 366). 



I must dissent from the words I have italicized. As often 

 as floating icebergs happen to touch a rocky bottom during 

 storms, when they are making way through the water like ships, 

 since they often weigh many thousands of tons, they will still 

 striate the bottom-rocks, although their own bottom parts will 

 be ground to powder by the operation. Such bottom parts 

 would do something in the way of striation, as Mr. Croll admits 

 (p. 367), by the mere force of concussion; for all their force 

 would not necessarily be expended in tearing up loose and dis- 

 jointed rocks, nor in hurling loose materials to a distance. 



In Jersey there are some remarkable striations or flutings on 

 the face of the metamorphic clayslate rock, which is nearly per- 

 pendicular, as you enter the village of PEtacq from the east, on 

 the right (i. e, the north) side of the road. They were first ex- 

 posed when the road was widened some eight or ten years ago. 

 Previously they were covered up with earth, grass, or other 

 rocks, I do not know which. I have heretofore spoken of these 

 as " slickensides '" but as they are horizontal, it is at least pos- 

 sible that they may have been striated by a glacier, as they are 

 at the side of a valley : — 



> 



Metamorphic-clay-slate section ; the 

 length 20 or 30 feet. 



