Bevieics — Prof. iV. 8. SJialer — On Glaciers. 37 



the interior of the earth, the weight of a mile of ice would bring 

 about pressure melting at the bottom of the glacier, and the parts 

 most deeply buried would from time to time be crushed into water. 

 This water, since its liquidity was due to pressure, would be only 

 free to move until it obtained a point where the pressure would be 

 sufficiently diminished to pennit its return to the solid state. There 

 would scarcely be any crevices in ice of this thickness, the result 

 would be that it would have to move horizontally along the junction 

 of ice and rock, if it moved at all. On this view the ice did not 

 move* from the far north southward as ice, but was driven out in the 

 form of water made liquid by pressure and friction. The erosive 

 power of this water carrying along stones and urged by the pressure 

 of the ice is considered as necessarily great. Besides other failings, 

 this theory seems to us to ascribe too much of the characteristic 

 glacial erosion to what is practically the movement of water rather 

 than of ice. It must be added that it is acknowledged by the author 

 as imperfect. A full explanation of this great continental ice-sheet, 

 if it existed, has yet to be given. It is pointed out that its analogue 

 must be sought in Greenland, but of the movements of the ice-iields 

 there little is known. 



We have passed over the discussion on the causes of the movement 

 of the Swiss glaciers, which we set down in tabular form with 

 objections and criticisms in a way that will be of great aid to 

 students. Similarly of the causes which have acted in bringing 

 about glacial periods. Dr. Croll's views are accepted in the main, 

 that the last glacial period was probably about 240,000 years ago — ■ 

 a time of great eccentricity, while according to this theory it ought 

 to contain mild interglacial periods in either hemisphere alternately. 

 We would direct readers to the chapter on the relation of glaciation 

 to Man, as one full of interest. The discovery of the Calaveras 

 skull in California, in gravel beneath lava currents, both of which 

 are older than the existing drainage channels, is quoted from Prof. 

 Whitney's original description. It is clear then that here Man was 

 Pre-Glacial if not Pliocene. Hence, as, according to Croll's hypo- 

 thesis, the last glacial period began about 240,000 years ago, and 

 commenced to pass away about 80,000 years ago, while the Pliocene 

 preceded the former in time, it follows that Man in California must 

 have had that exceeding antiquity. Our author seems not to shrink 

 from this conclusion. 



In the chapter on Ancient Glacial Periods will be found a further 

 extension of the argument from striated boulders than we are 

 accustomed to. It would seem that any great thickness of con- 

 glomerate is taken as prima facie proof of the existence of glaciers, 

 even though strige may not have been seen on the boulders. There 

 are said to be not less than a dozen periods where we have more or 

 less evidences of ice-action. We read, e.g. not only of Miocene and 

 Permian glaciers, but of Eocene, Triassic, Carboniferous, and Cam- 

 brian. The Carboniferous conglomerate series contain intercalated 

 beds of coal, a proof that the period was not one of general cold. 



The chapter on certain effects of glaciers, and their relation to 



