208 Dr. N. 0. HoM—The Glacial Period and 



No better success has attended the attempts to discover the cause 

 of the Glacial Period in directions other than that here indicated. 

 Especially is this true of the struggles after some far-fetched 

 astronomical explanation of this terrestrial phenomenon. The 

 geologist who perambulates the universe in searcli of such 

 explanations may be likened to an erudite bookworm who turns 

 his study upside down in search of his pencil, which all the time 

 is behind his ear. 



To the view here stated as to the cause of changes of level in 

 Glacial and Post-Glacial times, I have been led by my own researches, 

 and my ideas already tended in this direction before I realized that 

 T. F. Jamieson, and other geologists after him, had expressed views 

 almost identical with my own. Subsequently I have perused 

 Jamieson's writings on this subject more closely, and, with sincere 

 admiration for his acumen, have found that so early as 1865,^ 

 supported by comparatively few observations, he put forward the 

 leading idea which in 1882 - he developed in more detail, and which, 

 confirmed as it now is by more numerous observations, can without 

 hesitation be accepted as the only correct one. 



From the papers by Jamieson I think it right to make the 

 following instructive extracts : — 



" It has occurred to me [Jamieson] that the enormous weight of 

 ice thrown upon the land may have had something to do with this 



depression [the great glacial depression] We don't 



know what is the state of the matter on which the solid crust of 

 the earth reposes. If it is in a state of fusion, a depression might take 

 place from a cause of this kind, and then the melting of the ice 

 would account for the rising of the land, which seems to have 

 followed upon the decrease of the glaciers." (Q.J.G.S., loc. cit.) 



"Assuming the specific gravity of the ice to have been 875, 

 compared with water as 1,000, or in other words to have been 

 seven-eighths of the weight of water, then the weight of a mass 

 of ice 1,000 feet thick would be 378 pounds to the square inch, or 

 equal to fully 25 atmospheres, and would amount to 678,675,690 

 tons on every square mile. If the ice was 3,000 feet thick, it 

 would at this rate amount to over 2,000 million tons on the square 

 mile." (Geol. Mag., 1882, p. 403 ; Jamieson here quotes some 

 geologists who have supposed that the thickness of the ice has been 

 much greater, and then he continues as follows : — ) " It is evident 

 that a thickness of even 3,000 feet of ice will give us a weight hy 

 no means despicable, a weight which would require a marvellous 

 rigidity indeed in the earth beneath it to sustain such a load with- 

 out yielding in some degree " (p. 404). 



"That the crust of the earth is flexible and elastic the phenomena 

 of earthquakes sufficiently demonstrate. The surface heaves like 

 the billows of the sea, sometimes causing trees to bend so as to 



1 T. F. Jamieson, " Ou the History of the last Geological Changes in Scotland" : 

 Quart. Joiuu. Geol. Soc, 1865, xxi, p. 178. 



- " On the Cause of the Depression and Re-elevation of the Land during the 

 Glacial Period" : Geol. Mag., 1882, Dec. II, Vol. IX, pp. 400 and 457. 



I 



