CHAP. XIV. TIME REQUIRED FOR CHANGES OF LEVEL. 285 



■would best explain the successive fluctuations in teiTestrial 

 temperature, the glaciation of solid rocks, the transport- 

 ation of erratics above and below the sea-level, the height 

 of arctic shells above the sea, and last, not least, the migra- 

 tion of the existing species of animals and plants into their 

 actual stations, and the extinction of some conspicuous 

 forms which flourished during the post-pliocene ages. When 

 we duly consider all these changes which have taken place 

 since the beginning of the glacial epoch, or since the forest 

 of Cromer and the Elephas meridionalis flourished, we shall 

 find that the phenomena become more and more intelligible 

 in proportion to the slowness of the rate of elevation and 

 depression which we assume. 



The submergence of Wales to the extent of 1400 feet, as 

 proved by glacial shells, would require 56,000 years, at the 

 rate of 2^ feet per century; but taking Professor Eamsay's 

 estimate of 800 feet more, as stated at p. 267, that elevation 

 being required for the deposition of some of the stratified drift, 

 we must demand an additional period of 32,000 years, amount- 

 ing in all to 88,000 ; and the same time would be required for 

 the re-elevation of the tract to its present height. But if the 

 land rose in the second continental period no more than 

 600 feet above the present level, as in map, p. 279, this 600 

 feet would have taken another 26,000 years; the whole of the 

 grand oscillation, comprising the submergence and re-emer- 

 gence, having taken, in round numbers, 180,000 years for its 

 completion ; and this, even if thei'C were no j)auseor stationary 

 period, when the downward movement ceased, and before it 

 was converted into an upward one. 



I am aware that it may be objected that the average rate 

 here proposed is a purely arbitraiy and conjectural one, 

 because, at the Xorth Cape, it is supposed that there has been 

 a rise of about six feet in a century, and at Spitzbergen, 

 according to Mr. Lament, a still faster upheaval during the 



