THE GLACIAL PERIOD AND THE EARTH-MOVEMENT HYPOTHESIS. 247 



above the surrounding low grounds, or how, indeed, conti- 

 nents can rise above abysmal oceanic depressions. Professor 

 George Darwin has lately shown that the prominent in- 

 equalities of the earth's surface could not be sustained unless 

 the crust be as rigid as granite for a depth of 1,000 miles. 

 " If the earth," he remarks, " be solid throughout, then at 

 1,000 miles from the surface the material must be as solid as 

 granite. If it be fluid or gaseous inside, and the crust 1,000 

 miles thick, that crust must be stronger than granite, and if 

 only 200 or 300 miles in thickness much stronger than granite. 

 This conclusion is obviously strongly confirmatory of Sir 

 William Thomson's view that the earth is solid throughout," 

 Now if the crust have anything like the solidity attributed to 

 it by Professor Darwin — if there be no liquid stratum under- 

 lying a relatively thin crust, Mr. Jamieson's hypothesis cannot 

 be maintained. Theconnection between glaciationandsubmer- 

 gence, if it be not a mere coincidence, still remains, therefore, 

 to be explained. Recently, however, a newinterpretationof the 

 facts, which may possibly approve itself to physicists, has been 

 advanced by Dr. Dry gal ski. This author is of opinion that a 

 thick ice-sheet, by reducing the temperature of the underlying 

 crust, would cause this to contract, and so bring about sub- 

 sidence. The resulting depression of the surface would con- 

 tinue so long as the ice-sheet endured, but after it had 

 disappeared free radiation of earth-heat would be resumed, 

 the depressed isogeotherms would rise, and a general warming 

 of the upper portion of the lithosphere would take place. 

 But the space occupied by the depressed section, owing to 

 the spheroidal form of the earth, would be smaller than that 

 which it filled before sinking had commenced, and conse- 

 quently, when the ice vanished, expansion of the crust would 

 follow, and the land-surface would then rise again. But it 

 might not be able to attain its former elevation, and it is 

 quite conceivable that the amount of elevation might vary 

 throughout the newly risen area. If this explanation should 

 commend itself to physicists it would be welcomed by 

 geologists, for it is more readily reconcilable with the facts 

 than any other which has yet been advanced. Especially 

 would it throw some light on that irregular deformation to 

 which the region of the great lakes of North America seems 

 to have been subjected in glacial times. 



The advocates of the earth-movement hypothesis have 

 gladly hailed Mr. Jamieson's view as being in perfect harmony 

 with theirs. They are under the impression that it gets them 



