286 Prof. A. C. Ramsay on the Glacial Theory of Lake -Basins. 



this fact stated as a piece of common knowledge in a manual so 

 popular as Sir Charles LyelFs is sure to be. Some physical 

 geologists may doubtless marvel that Sir Charles, writing of 

 lakes that " run in great rents and faults," is still of opinion 

 that the existence of such rents and faults in connexion with 

 valleys " is no more than may be said of most of the longi- 

 tudinal and transverse valleys in every mountain-chain;" but 

 I will not argue that point, and I may forget the assump- 

 tion when I find it coupled with the admission of the truth of 

 the principle I endeavoured to establish, that mountain-lakes 

 do not lie in gaping fractures, and that fractures, wherever 

 we know them by eye, are almost always close*. Sir Charles, 

 I am glad to see, also approves of my argument to show 

 that the Alpine and other lake-basins are not the result of 

 special subsidences; and the admission of all these points by 

 him will help no doubt by-and-by to procure the adhesion of 

 readers who do not think or have no opportunity of observing 

 for themselves. Those who go so far take so many steps in the 

 right direction — steps, I think, which may in the long run lead 

 them to accept my theory altogether. 



But though there is this partial agreement in some details, 

 including the direct power of ice " in scooping out shallow basins 

 where the rocks are of unequal hardness - " (Antiquity of Man), 

 Sir Charles does his utmost to disprove the possibility of glaciers 

 on a great scale having been the means of scooping out by slow 

 erosion large lake-basins, such as those of the Alps, Scotland, 

 Sweden, or North America ; and I now propose, as briefly as I 

 can, to examine some of the arguments to which he seems to 

 attach the greatest weight. 



The erosion, then, of large rock-basins is untenable because 

 even if ice, in descending a steep slope, " scoop out one of 

 those cavities called tarns," yet we must suppose that it 

 loses all power of extending the cavity, being unable to cut 

 a gorge through the lower margin of the tarn ; and " this dimi- 

 nished force of erosion, wherever the ice has to ascend a slope, 

 or to move horizontally, seems adverse to the hypothesis of the 

 formation of lakes of considerable length and depth by glaciers." 

 In my last paper, published in the Philosophical Magazine 

 for October 1864, some months before the appearance of the 

 ' Elements/ I discussed for the second time what I believe to 

 have been the peculiar scooping effects of huge glaciers that issued 

 from the slopes of great, yet comparatively narrow valleys into 

 the wider plains that they overspread, or into flats near the 



* Attributed by Sir Charles to Mr. Jukes, who in an admirable article 

 in the ' Reader,' March 12th, 1864, used in my favour, and with new illus- 

 trations, the arguments which I employed in my original memoir. 



