272 GENERALIZATIONS. 



tion of land and water is far more important in reference to 

 climate than the greater or less excentricity of the earth's orbit, 

 and that so predominant an influence ought not to be attributed 

 to the variations of the orbit. 



The plants and animals that the rocks have preserved for us by 

 no means confirm Mr. CrolPs theory. It is only for the Quater- 

 nary period that the Swiss can admit a glacial epoch, interrupted 

 by the lignite formation of Utznach. As regards the geological 

 ages anterior to the Quaternary period, no facts sufficiently 

 well ascertained exist to enable Prof. Heer to draw the same 

 conclusions as Mr. Croll*. 



* Mr. Croll places the Quaternary (drift) glacial epoch between the years 

 240,000 and 80,000 before A.D. 1800 ; and lie supposes that the period of the 

 greatest excentricity of the earth's orbit which falls between the years 980,000 

 and 720,000 would correspond to a Miocene glacial epoch. But there is 

 nothing to support this hypothesis, unless, indeed, it be the remarkable ex- 

 istence of blocks foreign to the locality which occur in the Miocene deposits 

 of Superga, near Turin. Sir Charles Lyell is inclined to believe that these 

 blocks were transported by glaciers (see ' Principles of Geology, vol. i. p. 207). 

 These foreign blocks would have some analogy with the movement of the 

 immense icebergs which still advance southwards as far as Newfoundland. 

 But the presence of the blocks in the deposits of Superga is so isolated a fact 

 that it is hazardous to base upon these blocks the theory of a Miocene glacial 

 epoch, especially as the rocks which enclose them contain marine animals 

 and land plants possessing the same subtropical character as those of other 

 Miocene deposits. If at the Miocene epoch the country near Superga had had 

 a colder climate, its effects would have made themselves felt by the flora and 

 fauna, as is the case in the Quaternary glacial epoch. Mr. Croll places the 

 third period of great excentricity between the years 2,630,000 and 2,460,000, 

 which would correspond to the upper part of the Eocene. He supposes that 

 this epoch had a glacial period. 



In the Flysch rocks of this epoch large granite blocks occur in several parts 

 of Switzerland, belonging to a granite foreign to the Swiss Alps. They have 

 been considered in vol. i. pp. 256-270. The presence in the Flysch, at nume- 

 rous localities, of foreign blocks combined with great poverty in organic 

 remains is favourable to the hypothesis of Mr. Croll ; but his theory does not 

 rest upon data which have been scientifically investigated, and the facts are 

 capable of other explanations. Mr. Croll accounts for the absence of traces 

 of glacial periods in the older formations by modifications of the glacial soil 

 due to erosions, which destroyed the ancient soil of the continents, carrying 

 away with it all the debris of the glacial periods. Denudation has doubt- 

 less produced considerable modifications ; but their importance is not so great 

 as Mr. Croll imagines. Land deposits retain the masses of plants and animals 



