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



converted in some parts of their course into lakes of considerable 

 magnitude/' because otherwise we should have to assume " that 

 the greatest elevatory movement always conforms to the central 

 axis of every chain," or to that " of every watershed." " But 

 sometimes upheaval will be in excess in the lower part of the 

 valley, and at other times (which would equally produce lake- 

 basins) there would be an excess of subsidence in the higher 

 regions, the alluvial plains below sinking at a less rapid rate, or 

 being, perhaps, stationary." And here I must be allowed to 

 remark that these considerations did not escape me when I 

 wrote my memoir "On the Glacial Origin of certain Lakes "; but 

 I rejected them (I now see, unwisely) as random surmises, not 

 comparable in value to the various hypotheses I discussed, and 

 as I believe disproved, viz., that the great Alpine lakes " lie in 

 simple synclinal troughs," or in " areas of mere watery erosion," 

 or in mere " lines of dislocation," or " in areas of special sub- 

 sidence." I shall now show why I rejected and still reject both 

 of the above suppositions proposed in the ' Elements/ 



Referring to ' The Antiquity of Man/ Sir Charles very pro- 

 perly assumes that the large valleys of the Alps were of pre- 

 glacial origin, — a good and a sound assumption, founded on de- 

 finite proofs as old as the days of Charpentier, if not older, and 

 one I had occasion in this Magazine to show may have ori- 

 ginated in subaerial actions that have been going on ever since 

 the close of Miocene times *. No one, therefore, ever dreamed 

 that " the rivers had been idle for a million of years or more, 

 leaving to glaciers the task of doing, in comparatively modern 

 times, the whole work of excavation." But the question he 

 proposes to solve is, how, controverting my proposition of glacier- 

 erosion, parts of these valleys may have been converted into 

 lakes. Let us take the Lago Maggiore as an example. 



If in this case upheaval was " in excess in the lower part of 

 the valley," what would the result be ? 



From the deepest part of the lake to its efflux is a distance of 

 about twelve miles, and the average angle from the deepest part 

 to the efflux is 2° 21', and, giving every advantage to any one who 

 prefers upheaval " in excess in the lower part of the valley," I 

 will assume that the axis of movement lay on a line coincident 

 with the deepest part of the lake, or, in other words, that the 

 hinge, so to speak, of the movement lay there. Before the up- 

 ward movement began, the whole slope must have been down- 

 ward towards the valley of the Po, otherwise the drainage would 

 have been dammed up ; and it needs little reflection to see 

 in that case that the point which is now the efflux of the lake must 

 have been 2625 feet, or say 2650 feet lower than at present, so 

 * Phil. Mag. November 1862. 



