FAILURE OF CLIMATIC THEORIES. 11 



There has always been in Geology a tendency to 

 cataclysmic theories of causation ; a proneness to 

 attribute the grand changes experienced by the 

 earth's crust to extraordinary causes. Geologists 

 have only slowly become convinced that those changes 

 were the effects of the ordinary agencies in daily 

 operation around us. For example, hills were formerly 

 supposed to be due to sudden eruptions and up- 

 heavals ; valleys to subsidences, and deep river gorges 

 to violent dislocations of the earth. All this is now 

 changed, and geologists in general have become con- 

 vinced that the main features of the earth's surface 

 owe their existence to the silent, gentle, and continuous 

 working of such influences as rain and rivers, heat and 

 cold, frost and snow. 



It is not difficult to understand why a belief in 

 cataclysms should so long have prevailed, and geologists 

 should have been so prone to assume the existence of 

 extraordinary causes acting with great force. Geolo- 

 gical phenomena come directly under the eye in all 

 their magnitude, and consequently produce a powerful 

 impression on the mind. The quiet and gentle opera- 

 tions of nature's ordinary agencies appear utterly 

 inadequate to produce results so stupendous ; and one 

 naturally refers effects so striking to extraordinary 

 causes. Beholding in a moment the effect, we forget 

 that the cause has been in operation for countless 

 ages. 



We look, for example, at a gorge, perhaps a thousand 

 feet in depth, with a small streamlet running along its 

 bottom. Our first impression is that this enormous 

 chasm has been formed by some earthquake or other 

 convulsion of nature rending the rocks asunder ; and 

 it is only when we examine the chasm more minutely, 

 and find that it has been actually excavated out of the 



