236 The Great Ice Age and Origin of the “Till” [April, 
of larger masses of land that supply the required test- 
conditions. 
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 Switzerland 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 direct 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 favour 
of the ground moraine. 
I fully concur with Mr. Geikie’s arguments against the 
iceberg 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 con- 
nection 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 com- 
monly terminate in the form of a stream or cascade pouring 
down a “ moulin” or well bored by themselves and reaching 
the bottom of the glacier. Now what must be the acTion of 
such a downflow by water upon my supposed submarine bed 
* 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 Christania 
Fjord. The fjords, generally speaking, 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. 
