on the Bocks in the Environs of Edinburgh. 309 



left by a glacier slowly descending in a valley, and those 

 effected by floating icebergs carried along with a current, 

 but at the same time propelled by the winds, and buffeted by 

 the waves. Forces so exceedingly fortuitous and capricious 

 could scarcely ever produce that parallelism of striation 

 which has been ascertained to exist all around the Frith of 

 Forth. 



Striated Pebbles. — In examining the boulder-clay of Ross- 

 shire, Mr Hugh Miller observed that this deposit rested upon 

 polished and striated rocks, and that the pebbles contained 

 in the clay are, like those in the neighbourhood of Edinburgh, 

 covered with streaks. These streaks appeared to him to be 

 generally longitudinal, that is to say, parallel to the great 

 axis of the pebbles. Of this phenomena Mr Miller has found 

 an explanation which has a reference to the striation s both 

 of the rocks in situ and of the pebbles. Let us suppose, 

 says he, a great raft of wood descending a river, if it grazes 

 heavily upon a sunken bank covered with pebbles, reposing 

 upon a rock, it will propel them along without causing them 

 to roll, and then they will leave these striated marks upon 

 the rock in situ, and, in turn, will themselves be striated — 

 they will, according to a Scottish expression, be both 

 gcratchers and scratched. Put now a floating iceberg in the 

 place of a high raft of wood, and you have the explanation of 

 the striated pebbles of the boulder-clay of Scotland.* 



Notwithstanding the ingenious comparison of Mr Miller, I 

 cannot accept of his explanation. For I do not believe that 

 pebbles which are not incrusted in the ice could striate 

 rocks, and be in turn striated themselves. If that were the 

 case, we should find these striae in the bed of the impetuous 

 torrent of the Alps, or marks of pebbles upon the blocks so 

 often carried along at so rapid a rate. But never in these 

 torrents has any one shewed that the rock which forms its 

 bed, or that the pebbles therein contained, presented the ap- 

 pearance of s trice. They are polished, but never striated. 

 This is a fact which I have certified in the Alps, and also 

 on the sea-shore, where a striated pebble has never been 



* See the Scotsman newspaper, August 3, 1850. 



