IxXXVi PPvOCEEDI]SrGS OP THE GEOLOGICAL SOCIEir. 



SO great as to justify the conckisions of those wlio have attributed 

 to its action the excavation of basins in solid rock ma,ny hundred 

 feet in depth, and whether the position of these deep excavations 

 is such as any amount of glacial pressure could have produced 

 under any circumstances. 



The principal champion of the theory that the rock-basins in 

 which the Alpine lakes are placed were scooped out by the great 

 glaciers of the icy period, is Professor Bjamsay. He has supported 

 his views in three able publications *, with an amount of illustra- 

 tion and argument which might almost be said to carry conviction 

 to his readers ; and he has, to a certain extent, found a warm sup- 

 porter in Professor Tyndall in his paper " On the Conformation of 

 the Alps " in the same Number of the ' Philosophical Magazine.' 



Now it must be observed that there are here two questions 

 discussed, 1st, the erosion of the valleys themselves, and 2nd, the 

 scooping out of the rock-basins in which the great lakes have 

 been formed. With the former of these questions I do not pro- 

 pose to interfere. There is much force in Professor Tyndall's 

 argument, drawn from the great regularity of feature which per- 

 vades the system of valleys in a mountain-chain, showing the 

 probability that much of this system was the result of the eroding 

 force of water and of ice combined Avith the general effects of 

 weathering ; but it should, I think, be conceded that this agency 

 must have been greatly assisted by the varied nature of the 

 material which was to be eroded, and the extent to which the 

 ' mountain masses had been previously dislocated and contorted by 

 the many changes — upheavals, depressions, fractures, inversions, 

 and other disturbances, which there is abundant evidence to show 

 they must have undergone in previous geological periods of almost 

 infinite duration. "We have only to look at the different configu- 

 rations of land and sea in Switzerland alone, so graphically de- 

 scribed by Professor Heer of Zurich, to be convinced of the truth 

 of this statement. 



The question, therefore, to which I mean to confine myself at 

 present is the scooping-out of the rock-basins by glaciers. Pro- 

 fessor Ramsay in his paper in the Society's ' Journal,' after 

 disposing of four distinct hypotheses as to the cause of lake-de- 

 pressions or hollows, namely, a synclinal trough, a line of fracture, 

 an area of subsidence, or an area of aqueous erosion, concludes 

 that the great moulding agency of ice is the ojilt/ other cause by 

 which the form of the ground could have been thus modified. 

 Now it appears to me that Professor Eamsay has too hastily 

 assumed the impossibility of any of these four causes having had 

 anything to do with the formation of lake-basins. It is true that 

 the evidence he brings forward against the operation of any one 

 of these causes in each particular case alluded to may be correct, 

 but it does not therefore follow that he is correct in stating that 

 none of these causes could have operated in any case. It does 



* Quart. Journ. Oreol. Soc. vol.xviii. p. 185 ; Physical G-eography and Geology 

 of Great Britain ; and the Philosophical Magazine, vol. xxviii. p. 293. 



