ISO SCIENCE IX SHOKT CHAPTEHS. 



From the above it will be seen that I agree with Mr. 

 Geikie in regarding the till as a moraine profonde, but differ 

 as to the mode and place of its deposition. He argues that 

 it was formed under glaciers of the thickness he describes, 

 while their whole weight rested upon it. 



This appears to me to be physically impossible. If such 

 glaciers are capable of eroding solid rocks, the slimy mud of 

 their own deposits could not possibly have resisted them. The 

 only case where this might have happened is where a mountain- 

 wall has blocked the further downward progress of a glacier, or 

 in pockets, or steep hollows which a glacier might have 

 bridged over and filled up ; but such pockets are by no means 

 the characteristic localities of till, though the till of Switzer- 

 land may possibly show examples of the first case. The great 

 depth of the inland lakes of Norway, their bottoms being 

 usually far below that of the present sea-bottom, is in di- 

 rect contradiction of this.* They should, before all places, 

 be filled with till, if the till were a ground moraine formed on 

 land ; but all we know of them confirms the belief that the 

 glaciers deepened them by erosion instead of shallowing them 

 by deposition. 



Mr. Geikie' s able defence of Ramsay's theory of lake-basin 

 erosion is curiously inconsistent with his arguments in favor of 

 the ground moraine. 



I fully concur with Mr. Geikie's arguments against the ice- 

 berg theory of the formation of the till. This, I think, he has 

 completely refuted. 



Before concluding I must say a few words on those curious 

 lenticular beds of sand and gravel in the till which appear so 

 very puzzling. A simple explanation is suggested in connec- 

 tion with the above-sketched view of the formation of the till. 

 All glaciers, whether in arctic or temperate climates, are 

 washed by streamlets during summer, and these commonly 

 terminate in the form of a stream or cascade pouring down a 

 moulin a well bored by themselves and reaching the bottom 

 of the glacier. Now what must be the action of such a down- 



* The largest of the Norwegian lakes, the Mjosen, is 1550 feet 

 deep, and its surface 385 feet above the sea level. Its bottom is 

 about 1000 feet lower than the sea outside, or 500 to 800 feet below 

 the bottom of the Christiania Fiord. The fiords, generally speak- 

 ing, are very much shallower near their mouths than further inland, 

 as though their depth had been determined by the thickness of the 

 glaciers flowing down them, and the consequent limits of flotation 

 and deposition. 



