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



feet in 6000 years ; and this might be much more than we require, 

 for allowing longer time far less than this might be enough. Now 

 an inch in the year is less than a hair's breadth in the day. 



The earth's diameter is about 7900 miles, which is equal to rather 

 more than 500 million inches. Suppose then we had a pile of 

 books consisting of a million volumes, each containing 1000 pages, 

 a compression of an inch would be represented by the thickness of 

 only a single leaf or -g-oTT,oo-o,oo-o part of the whole. Now for a 

 depi'ession of an inch we may allow at least a whole year and 

 perhaps even five years. The action we invoke therefore does not 

 seem to be an unreasonable or extravagant one. 



The recovery of level after the ice disappeared would depend 

 upon the elasticity of the materials beneath the depressed region. 

 The rise would probably be very slow and gradual, like the depression, 

 and in many cases the recovery of level would probably be incom- 

 plete. The unequal strength of the earth's crust and the irregular 

 way in which it yields to pressure are exemplified by what we know 

 about faults. 



Faults are often of great magnitude, extending sometimes to many 

 hundred feet and occasionally, it has been supposed, to even thousands 

 of feet ; and they show that the subterranean structure may be such 

 as to give way very unequally to pressure. It has been thought that 

 subterranean cavities exist which might allow a permanent amount 

 of subsidence to be effected with comparative ease. 



The general paucity of animal remains in the marine beds of the 

 Glacial period would seem to indicate that the actual occupation of 

 the surface by the sea- waters had not been very prolonged, for had it 

 been so, we should expect to find remains of whales, seals, and fishes, 

 far more abundantly than we do, and also great beds of sea shells. 



Animal life swarms in many parts of the Arctic Ocean, and we 

 can hardly suppose the sea to have occupied our coasts for thousands 

 of years without leaving remains of marine life in a degree of plenty 

 far beyond what we find in any of the Glacial-Marine beds of this 

 country. During the commencement and earlier stages of the 

 depression the submerged tracts which are now above water would 

 probably be occupied by glacier-ice, and it would only be after the 

 ice broke up and floated off that the sea would take its place, by 

 which time the land would be on the rise again. The subsidence of 

 the land no doubt contributed much to the dispersion of the ice by 

 enabling it to float away and get melted in warmer water. 



If the glacial conditions were simultaneous in the north and south 

 hemispheres during the age of ice, there can be little doubt that the 

 abstraction of so great a mass of water from the ocean, together 

 with the contraction in bulk of the water owing to the colder 

 temperature, would have very sensibly lowered the sea-level, as Mr. 

 Alfred Tylor pointed out.^ But owing to the want of proper data 



1 Geol. Mag. 1872, pp. 392 and 485. Mr. Alfred Tylor calculated that a 

 deposit of snow and ice loOO feet thick over an area of land one-tenth of that of the 

 sea, would reduce the level of the ocean 150 feet. He supposes a subsidence of 

 600 feet altogether. 



