INTERPRETATIONS OF ICE-AGE 179 



freely made without impairing the real value of the 

 Huttonian doctrine, that in the interpretation of this 

 history our main guide must be a knowledge of the 

 existing processes of terrestrial change. 



As the most recent and best known of these great 

 transformations, the Ice-Age stands out conspicuously 

 before us. If any one sixty years ago had ventured 

 to affirm that, at no very distant era in the past, the 

 snows and glaciers of the Arctic regions stretched 

 southwards to the Bristol Channel and the basin of 

 the Thames, he would have been treated as a mere 

 visionary theorist. Many of the facts to which he 

 would have ' appealed in support of his statement were 

 already well known, but they had received various 

 other interpretations. By some observers, notably by 

 Hutton's friend, Sir James Hall, they were believed 

 to indicate violent debacles of water that swept over 

 the face of the land. By others they were attributed 

 to the strong tides and currents of the sea when the 

 land stood at a lower level. The uniformitarian school 

 of Lyell had no difficulty in elevating or depressing 

 land to any required extent. Indeed, when we con- 

 sider how averse these philosophers were to admit 

 any kind or degree of natural operation other than 

 those of which there was some human experience, we J 

 may well wonder at the boldness with which, on 

 sometimes the slenderest evidence, they made land 

 and sea change places, on the one hand submerging 

 mountain-ranges, and on the other placing great 

 barriers of land where a deep ocean rolls. They 

 took such liberties with geography because only well- , 

 established processes of change were invoked in the 



