122 GEOLOGtCAL CHANGE, AND TIME. 



this globe. Such occurrences might never seriously affect the whole 

 earth at one time, and might return at such wide intervals that no ex- 

 ample of them has yet been chronicled by man. But that they have 

 occurred again and again, and even within comparatively recent geologi- 

 cal times, hardly admits of serious doubt. How far at different epochs 

 and in various degrees they may have included the operation of cosmi- 

 cal influences lying wholly outside the planet, and how far they have re- 

 sulted from movements within the bod}' of the planet itself, nuist remain 

 for further inquiry. Yet the admission that they have played a part in 

 geological history may be freely made without imi)airii]g 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 date the snows and 

 ghiciers of the Arctic regions stretched southwards into France, he 

 would have been treated as a mere visionary theorist. Many of the 

 fiicts to which he would have api)ealedin supi)ortof his statement were 

 already well known, but they had received various other interpretations. 

 By some observers, notably by Hutton's fi'iend, Sir James Hall, they 

 were believed to be due to 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 uni- 

 formitarian school of Lyell had no difficulty in elevating or depressing- 

 land to any required extent. Indeed, when we consider how averse 

 these philosophers were to admit any kind or degree of natural opera- 

 tion other thiui those of which there was some human experience, we 

 may well wonder at the boldness with which, on sometimes the slender- 

 est 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 geogra- 

 phy because only well-established processes of change were invoked in 

 the operations. Knowing that during the passage of an earthquake a 

 territory bordering the sea may be upraised or sunk a few feet, they 

 drew the sweeping inference that any amount of upheaval or depression 

 of any part of the earth's surface might be claimed in explanation of 

 geological i>roblems. The ]>rogress of inquiry, while it has somewhat 

 curtailed this geographical license, has now made known in great detail 

 the strange story of the Ice Age. 



There can not be any doubt that after man had become a denizen of 

 the earth, a great physical change came over the Northern hemisphere. 

 The climate, which liad previously been so mild that evergreen trees 

 flourished within ten or twelve degrees of the north pole, noAv became so 

 severe that vast sheets of snow and ice covered the north of Europe and 

 crept southward beyond the south coast of Ireland, almost as far as the 



