RESUME AND GENERAL DISCUSSION. 393 



then it is not possible that the evidence should all be on the side of diminu- 

 tion of temperature with the progress of the geological ages. Yet such, in 

 reality, appears to be the case. While all will admit that the proofs of a 

 former higher temperature in various regions in pre-Glacial times are mani- 

 fold and such as cannot possibly be set aside, it will be found impossible 

 to show anything of essential importance of an opposite character. Nor has 

 such proof at any time been brought forward by the advocates of cyclical 

 changes of climate. 



The principal support of the theory of a succession of Glacial epochs dur- 

 ing the geological ages is to be found in the alleged occurrence of a few 

 boulders in some of the older formations, striated in a manner resembling the 

 work of ice during the Glacial epoch proper. AVhen, however, Ave consider 

 that mas.'^es of earth or of rock having boulders projecting from their sides 

 or bottoms must be striated when forcibly moved in contact with hard sub- 

 stances, and when we reflect that such motion must occasionall}-, if not often, 

 have taken place under other circumstances than those connected with the 

 existence of moving ice masses, it becomes evident that striation is not a 

 sufficient proof of an entire change of climatic conditions such as is demanded 

 by the cyclical theory here under discussion. Every one familiar with the 

 interior of mines has had occasion to see repeatedly, and as one of the com- 

 monest of phenomena, how striated surfaces are produced by motion of rock 

 masses against each other ; and it is easy to understand liow fragments of 

 such striated materials might become loosened from their fixed position, and, 

 after being more or less acted on by water or other erosive agencies, take on 

 an appearance not easily to be distinguished from that presented by pebbles 

 or boulders which have been actually striated by ice. 



The inspection of the bed of almost any recent great rock avalanche in a 

 mountain region will not fail to result in the discovery of striated and 

 scratched surfoces which from their freshness and other characters will be 

 recognized at once, by an experienced eye, as having been foinied by the 

 slide itself.* 



Some even go so far as to see the work of ice in every accumulation 



* The writer examined with rare, many years ago, the locality of the great avalanche mentioned by Dante 

 (Inferno, XII. 4, 10), called I Slavini di .San iMareo, and which probaldy took place in 845. It is on the route 

 from Trent to Verona. Here the scorings and striation of the tract over which the avalanche passed, more than a 

 thousand years ago, are still most conspic-uous. Their charaeter, position, and direction with regard to the line of 

 the fallen masses of rock are such that there can be no question as to their nature, or as to tlicii having been 

 rcallv made by the avalanche itself. 



