Prof. A. C. Ramsay on the Glacial Theory of Lake-Basins. 293 



as to bring it at the least to a level a little lower than what is 

 now the deepest part of the lake. Without this the onward 

 southern flow of the water could not have been established. 

 But in that case the plain of the Po outside the present efflux 

 of the lake must also have been at the least 2650 feet lower than 

 at present, that is to say, before the tilting began ; in which 

 case the plain must have been about 2000 feet below the level of 

 the present sea, and liable to be covered with deposits of that 

 post-pliocene epoch. But no trace of these deposits exists, 

 and they have never even been imagined ; for the post-pliocene 

 deposits of the valley of the Po are older than the ancient 

 glaciers. The only escape from this is to suppose that when these 

 movements took place the whole region lay so high (from 2000 

 to 3000 feet higher than at present) that elevations and de- 

 pressions had no immediate relation to existing sea-levels. 



But though Sir Charles alludes to upheaval " in excess in 

 the lower part of the valleys," he rejects it in the case of the 

 Alpine valleys, and prefers another hypothesis to account for 

 the actual existence of the lakes as they now stand ; and this I 

 shall now examine. 



"The Alps," he observes, "are from 80 to 100 miles 

 across. Let us suppose a central depression in this chain at the 

 rate of 5 feet in a century, while the intensity of the move- 

 ment gradually diminishes as it approaches the outskirts of the 

 chain, till at length it dies out in the surrounding lower region." 

 Thus in time the valley-slopes that originally all declined out- 

 wards and downwards from the central elevations of the moun- 

 tains, would in the lower regions, by depression of the central 

 ridges, by degrees acquire a reverse slope, that is to say, towards 

 their ends they would slope inwards to the mountains, and by 

 this process the drainage would become dammed up by rock, and 

 lake-basins would be formed. Now, to test this idea, we must take 

 the distance between the efflux of lake and lake on the opposite 

 sides of the chain. Prom the outflow of the Lago Maggiore to 

 that of the lake at Lucerne, the distance is roughly about ninety- 

 three miles in a straight line ; and if we measure another line 

 as far as the north end of the Lake of Zurich, the distance is 

 about 112 miles. It will make no material difference in my 

 argument which line I take ; but let us take the latter, for it is 

 clear that the rule of subsidence ought to apply to the lakes in 

 general on both sides of the Alps. A point halfway between 

 the outflow of the Lake of Zurich and that of Maggiore lies near 

 the upper end of the valley of the Rhone, that is to say, just 

 about the main centre of the Alpine chain. The distance, then, 

 from the south end of the Lago Maggiore to the central point 

 of subsidence in the Alps was about fifty-six miles. Now the 



