DATE SUGGESTED FOR THE GLACIAL EPOCH. 411 



to assign C than B as the period in question ; " in other words, 

 to regard the glacial epoch as representing a period 800,000 



'o 



years ago." 



In differing from such a great authority as Sir C. Lyell, 

 I do so with great diffidence, but I confess that I should be 

 disposed rather to assign the glacial era to the periods A and B, 

 than to either C or D. * 



It seems to me unlikely that the present fauna of Europe 

 should have continued to exist, almost without alteration, for 

 so long a period as 800,000 years, and the " variations in the 

 range and distribution of aquatic and terrestrial animals," 

 might, I think, have occurred in even less than 200,000 years 

 under the great changes in climate which have taken place. 

 Moreover, the Geological Magazine for June, 1868, contains an 

 interesting paper by Mr. Geikie, " On Denudation now in 

 Progress," in which he discusses the general effect produced 

 by rivers in excavating valleys and lowering the general level 

 of the country. "For it is clear that if a river carries so 

 many millions of cubic feet of sediment every year into the 

 sea, the area of the country drained by it must have lost the 

 quantity of solid material, and if we could restore the sedi- 

 ment so as to spread it over the basin, the layer so laid down 

 would represent the fraction of a foot by which the basin had 

 been lowered during a year/' From observations made on 

 the Mississippi, Ganges, Ehone, Danube, and other great rivers, 

 Mr. Geikie estimates the annual loss at & ^ 00 of a foot. But 

 he points out that this would not be uniform. The plains 

 and watersheds would lose little, the slopes and valleys much. 

 "There can be no doubt," he says, "that the erosion of the 

 slopes and water-courses is very much greater than that of 

 the more level grounds. Let it be assumed that the waste is 

 nine times greater in the one case than in the other (in all 

 likelihood it is more) : in other words, that while the plains 



* MivCroll has also expressed this opinion. Phil. Mag. 1868, p. 367. 



