of Valleys and Lakes. 307 



how awfully high and rugged they are ; can any amount of time, 

 aided by weather, torrents, rivers, and glaciers produce such 

 effects ? Old writers, like Hutton and Playfair, and a few 

 modern observers (some of whom, both in America and Europe, 

 have great familiarity with rocks), say they can; but we know that 

 rending and fracture is the chief agent, and denudation is in com- 

 parison quite a trifling affair. Look, again, at the hollows of the 

 lakes, how awfully deep they are ! How is it possible for a glacier 

 ever to have slid up a hill from a depth so profound ? " In 

 treating the slopes as great, consists the viciousness of this sup- 

 posed argument. Unconsciously, some of the arguers are draw- 

 ing exaggerated diagrams in their minds. They foreshorten the 

 slope, increase in their mind's eye its steepness, and forget 

 their trigonometry altogether. But let me beg of them to try 

 to realize the real state of the case, and see how small by com- 

 parison the depth really is, and how gentle the slope. Were 

 the bottom of the Lago Maggiore not undulated (for I believe 

 the islands to be mere roches moutonnees) , this slope from the 

 deepest part of the lake (2600 feet) to its outflow would only 

 be 2° 21' in a distance of about 12 miles, a slope so gentle that, 

 were a man standing on it, by the eye he would barely be able 

 to tell whether he was on an inclined plane or not*. Again, 

 take the Lake of Geneva from the place where it is nearly a 

 thousand feet deep to Geneva, the average slope is only about 

 25', an angle so small that any geologist looking at it would be 

 apt to consider the surface as horizontal. The question, then, 

 as regards the lakes resolves itself into this : Is it possible that 

 the ice of the great old glaciers could ever have travelled up 

 these exceedingly small inclinations for a distance, say of 12 

 miles in the one case and 20 to 25 miles in the other ? 



And now, in connexion with this point, I could wish that Sir 

 Roderick had expressed an opinion whether or not he agrees 

 with the old geologists, that (p. 7) " the Lakes of Geneva and 

 Neufchatel were so filled up with snow and ice that the advancing 

 glaciers travelled on them as bridges of ice, the foundations of 

 which occupied the cavities." If this were so, then, in other 

 words, the lower strata of ice in the hollow of what is now a 

 lake remained in a condition of static equilibrium, and over this 

 ice the advancing part of the glacier slipped or was propelled. 

 Strictly speaking, it is evident that this state of static equilibrium 

 is impossible ; for all the ice of a glacier a little below the sur- 

 face being, even in winter, in a melting state, the lower strata 



* In my original paper on the glacial excavation of certain lakes, I 

 made an unfortunate error in calculation, stating that the angle is about 5°. 

 In an able article in the ' Reader,' Professor Jukes corrected the error, and 

 made the slope 2°. 



