166 PEOCEEDINGS OF THE GEOLOGICAL SOCIETT. [Feb. 26, 



be again referred to in a subsequent part of this paper. But in no 

 case could I discover the least indication of any such polish, or 

 straight parallel scratching, due to the action of the torrent ; I 

 observed, however, in some places on the surface of the greenstone, 

 many round pits or dints, and short irregular scoops or furrows, 

 seldom longer than a man's fuiger, caused apparently by the bumping 

 of the large boulders as they rolled along. These markings were 

 irregular in their direction, like the scratching of poultry on a gravel 

 walk, and quite unlike the long, rectilinear, parallel grooves and 

 the polish which are ascribed to the action of ice. Here, then, it was 

 evident that not only had this violent torrent no power to cause such 

 markings, but, from the shortness of its duration, it had also failed 

 in most places to obliterate the real glacial markings of a former 

 period. 



Agassiz likewise mentions that the debacle of the Dent du Midi — 

 another example of a current of water charged with fragments of 

 rocks — left no trace of this kind in any part of its course*. 



§ 3. In 1837, the Swiss naturalist whom I have just mentioned com- 

 municated to the Academy of Sciences at Paris some observations on 

 the mode in which glaciers thus affect their rocky bed ; and his force 

 of character, together with the ardour he threw into the pursuit, 

 effectually roused attention to the subject f. In 1840 (nearly 30 years 

 after Imrie and Hall wrote) he paid a visit to this country, and, in an 

 extensive tour through Britain and Ireland, everywhere recognized 

 in our rounded, scored rocks appearances precisely similar to those 

 he had long studied among the glaciers . of his native country ; and 

 he did not hesitate to express his comiction that in Britain glaciers 

 and large sheets of ice, " resembling," as he says, " those now exist- 

 ing in Greenland," had formerly existed, to whose action these 

 markings are due. The occurrence, however, of marine remains 

 belonging to the Pleistocene period at various elevations, and even on 

 the tops of considerable hills, together with a great mass of collateral 

 evidence which went to show that this country had been to a great 

 extent depressed beneath the sea during the Drift-period, led many 

 to believe that the appearances referred by Agassiz to glacier- action 

 might be better accounted for by the agency of floating ice ; while 

 the absence of alpine heights, and the comparative lowness of much 

 of the country where these markings occurred, still further conduced 

 to this opinion. ; ; , 



When, therefore, I began the study of < the subject, it was rather 

 with a disposition to refer these appearances to sea-borne ice ; but a 

 careful examination of such instances as have come under my notice 



* The observations of Lyell on the Willey Slide in the Wliite mountains of 

 North America, and those of Dr. Hooker in the Himalaya, go to show that even 

 land-slips do not mark the rocks over .which they pass in the same way that a 

 glacier does. - '; 



t Although Charpentier, and perhaps others, had previously mentioned the 

 erosive action of glaciers upon their rocky bed, yet Agassiz comprehended better 

 than any the geological importance of the phenomenon ; and he seems to have 

 been the first to draw attention to the marked distinction that exists between the 

 features of ice-worn and those of water- worn rocks. 



