T. F. Jamieson — Oscillation of Land in Glacial Period. 405 



tinental dimensions seems to me very improbable indeed. It appears 

 more likely that the position of the surface is in a state of delicate 

 equilibrium, and that any considerable transference of pressure will 

 cause a re-adjustment of levels. If upheavals and depressions of 

 the land have not been caused by changes of pressure, it may be 

 asked what is it they have been caused by ? In volcanic eruptions 

 even so slight a difference in pressure as the varying weight of the 

 atmosphere has been thought to have some influence on the subter- 

 ranean forces. The elasticity of the ground is so great indeed as to 

 respond to very insignificant agencies. The rumbling of a waggon 

 along the street, the galloping of a troop of horse, or even the 

 measured tread of armed men, causes a vibration of the surface 

 which is plainly felt. 



If beneath that part of the surface which was affected by the heavy 

 pressure of the ice there happened to be a quantity of lava in a fluid 

 state, the result might be to cause an outburst of the lava to take 

 place at some more distant point. This would relieve the tension 

 and lead to a permanent depression of the ice-covered area. For 

 example, in North America, the great fields of ice that lay on certain 

 portions of that continent by their downward pressure may have 

 occasioned some of those extensive eruptions which seem to have 

 taken place in the region of California after the commencement of 

 the Grlacial Period.' The volcanic phenomena of Iceland in like 

 manner may have been affected by similar causes. That there has 

 been a considerable permanent depression of some of the most heavily 

 glaciated regions since the commencement of the Glacial period 

 I think there is much reason to believe. The features of the Fiord 

 districts of Norway and the West Highlands of Scotland and of 

 British Columbia, for example, seem to show this ; for these coasts 

 have all the appearance of depressed mountain lands, which have 

 been cut and carved by streams and glaciers far beneath the present 

 level of the sea. The glaciation of the United States also presents 

 some singular features that seem to point to an elevation of the 

 Canadian ridge between the lakes and Hudson's Bay much greater 

 than now exists. 



But in regard to the effect of pressure, time is an important 

 element in the problem. 



Bodies that seem absolutely rigid to pressure applied for a short 

 space of time yield perceptibly to a force which is long continued. 

 The effect may be so minute as to be quite imperceptible at first, yet 

 when multiplied a sufficient number of times it will give us all that 

 we require. And this is just the lesson that Geology has so often 

 impressed upon us. Now in the case we are considering we can 

 draw lai'gely on the Bank of Time. 



In regard to the pressure exerted by the ice, we must bear in mind 

 that it probably continued for very many thousands of years. If 

 we suppose that it caused a depression of only an inch in the year, 

 this would give us a foot in 12 years, 100 feet in 1200 years and 500 



' See J. Le Conte, On the Old River Beds of California, in the American Journal 

 of Science, for March, 1880. 



