PROOFS OF ITS EXISTENCE. 239 



posited under the ordinary conditions of water, that they 

 belong especially to the northern hemisphere, have been 

 drifted from a northerly source, and in all likelihood by 

 ice partly on land and partly in water.* The older terms 

 " diluvium " and " diluvial drift," under the idea that they 

 were the results of the Noachian deluge, have been long 

 ago set aside, and geologists with one consent now look to 

 ice, in one or other of its manifestations, as the only known 

 agent by which they could have been accumulated. Eain 

 and rivers can, no doubt, waste and wear down the land, 

 but it is ice alone that can grind and smooth and confer 

 those rounded outlines which characterise so much of the 

 surface in the higher latitudes of the northern hemisphere. 

 River floods and freshets can accumulate vast mounds of 

 sand and shingle ; but it is the glacier alone that throws 

 across the glen its dam-like moraine, and scores and polishes 

 the pebbles of which it is composed. Running water laden 

 with debris will wear and smooth the rock-surfaces over 

 which it flows ; but it is ice alone that can put on the glassy 

 polish, and scratch and gouge in long straight furrows with 

 its imbedded blocks and fragments. Rivers and torrents 

 will roll and transport blocks of considerable size ; but it is 

 ice alone, either as the ice-sheet on land or the iceberg on 

 water, that can tansport boulders many tons in weight up 

 and over hills, or float them away hundreds of miles from 

 their parent precipices. Running water invariably assorts 

 its debris in beds and layers according to its fineness ; it is 

 floating ice alone that drops its burden on the sea-bed with- 

 out regard to arrangement. All these appearances boulder- 



* Objection has been taken to each and all of these designations, and 

 it must be confessed we are still in want of a good general term for the 

 accumulations of the glacial epoch. Drifts, erratic blocks, and boulder- 

 clays, are but members of a great series, and it is for this series, taken 

 as a whole, that we still stand in need of a comprehensive designation. 



