Prof. A. C. Ramsay on the Glacial Theory of Lake- Basins. 297 



would approach the lowest of these numbers; while if we 

 shorten the line still more, and place it at the Borromean Islands, 

 we then get merely a special sinking of the bottom of the lake, 

 — that for Maggiore, making no allowance for sediment, being 

 2625 feet. Considering, however, that the depression of the 

 chain, according to Sir Charles LyelFs hypothesis, ought to have 

 been the means of forming the rock-basins on both sides of the 

 Alps, it is difficult to get rid of the idea that a great central 

 depression was the cause, if there be any ground for the idea 

 at all. In that case Charpentier's 3000 feet come very far 

 below the mark. Indeed, if we must allow 14,000 feet of depres- 

 sion to form the lake- basins (still full of ice), one cannot see 

 why there are not a great many more lakes than we find ; for they 

 ought also to occur in other valleys that run north and south of 

 the central chain and open on the plains, but which are merely 

 river- courses. 



Again, how do the existing lakes conform to the regulation ? 

 Certainly those of Geneva and Neuchatel do not in their trend 

 agree with a supposed depression of the Central Alps ; for their 

 lengths and outflows are, roughly, at right angles to those of the 

 other great lakes of Como, Lugano, Maggiore, Orta, Varese, 

 Garda, Thun, Lucerne, Zug, Sempach, Zurich, and Constance; 

 and to dam up the lakes of Geneva and Neuchatel, we should 

 require a central depression running north-west between them 

 at right angles to the chain of the Alps, and quite across the 

 Miocene rocks. For this we need a special proof, which has 

 never even been attempted ; and I do not see but that to produce 

 the whole of the lakes by depression, the supposed great move- 

 ment must merely resolve itself into a number of minor ones. 

 A better supposition than this seems to me to be a special dis- 

 location, or a special depression for each lake, which I have 

 elsewhere attempted to disprove. 



And now, to sum up the matter, let us see what I am ex- 

 pected to allow if I am forced to accept as proved the adverse 

 points that have been raised against my theory. The Alps 

 " may have been at the time of intense cold 3000 feet higher 

 than they are now. They may also have been lower again." 

 "The repetition of such unequal movements may, in a time 

 geologically brief, turn parts of a valley into a lake." "If 

 there be no ice during the movement, &c," and "should the 

 movement be very slow," " the river may afterwards fill up the 

 cavity," and "it may afterwards cut through the new stony 

 barrier." " If the change takes place in a glacial period, the 

 thickness of the ice will augment from century to century, not 

 in consequence of erosion, but simply because the contour of 

 the valley is becoming gradually more basin-shaped. The mere 



Phil. Mag, S. 4. Vol. 29. No. 196. April 1865. X 



