1865.] Geology and Palceontology. 479 



is such as any amount of glacial pressure could have produced under 

 any circumstances." He distinctly separates the erosion of valleys 

 from the excavation of lakes, as being two distinct questions, and his 

 remarks apply only to the latter. 



One President attempts to expose a logical fallacy in the argu- 

 ments of the other, thus : — According to Mr. Hamilton, Professor 

 Eamsay strives to show that neither a synclinal trough, a line of frac- 

 ture, an area of subsidence, nor an area of aqueous erosion could have 

 formed the sites of the Alpine lakes, because one is incompatible with 

 existing conditions or phasnomena in one case, another in a second, and 

 so on, and that the action of ice is the only other cause by which the 

 form of the ground could have been so modified ; were this so, Mr. 

 Hamilton would be quite right in saying, " it does not follow, for in- 

 stance, that because the Lake of Geneva does not lie in a synclinal 

 trough, it may not be in an area of depression, or that because the Lake 

 of Garda is not in an area of depression, it may not be in a line of 

 fracture." But, if we rightly understand Professor Ramsay, he is 

 scarcely guilty of such an extraordinary piece of sophistry, for it seems 

 to us that he endeavours to show that there is presumptive evidence 

 against any of the lake-basins having been produced by any of the 

 causes mentioned, the action of glaciers excepted. He does not take 

 one cause for one lake, another cause for a second, &c, and then draw 

 a general conclusion from particular premises. But this question has 

 only a collateral bearing on that of the power of ice to excavate such 

 rock-basins. 



There seems to be much more force and justice in another of Mr. 

 Hamilton's series of arguments. He combats the idea of a glacier 

 beiDg able to excavate a great rock-basin like that of the Lake of 

 Geneva, after having emerged from a comparatively narrow gorge-like 

 valley into a vast plain, where it must have reached a state of compa- 

 rative, if not absolute rest ; and he also urges that if the vis a tergo be 

 what it is represented (of which, by the way, he seems very sceptical), 

 and if it did force the ice into and along the plain, then the upjDer 

 portion of the glacier would be forced over and along the lower, which 

 would remain almost stationary. Professor Eamsay has stated that he 

 " cannot conceive a horizontal fracture of forty miles in length over 

 the area of the Lake of Geneva, clearly dividing two bodies of ice, the 

 lower of which was when thickest nearly 1,000 feet, and the upper and 

 sliding stratum must have been nearly 3,000 feet thick." Mr. Hamil- 

 ton, however, states that the meaning is simply that the motion of 

 the ice of a glacier resembles that of the water of a river, being fastest 

 in the centre of the stream at the surface, with a gradual diminution 

 towards the bottom and sides. This kind of motion seems entirely 

 in accordance with natural laws, and quite fatal to the glacier- 

 excavation theory. 



Dr. Haast's papers contained in the same number of the ' Quarterly 

 Journal ' also relate to this subject ; their titles are as follow : — 



1. " On the Causes which have led to the Excavation of deep Lake- 

 basins in hard Rocks in the Southern Alps of New Zealand." 



2. " On a Sketch-map of the Province of Canterbury, New Zealand, 



