242 THE GLACIAL OE ICE EPOCH. 



and strise produced by the mountain-glacier can give no 

 idea of the direction of the current that bore the iceberg ; 

 and the ploughings of the iceberg through firth and strait 

 can give no indication of the course of the glacier from 

 which it was detached. The fact is, that the direction of 

 these groovings and gougings must be read each in the light 

 of its own locality ; and we have seen on many rock-sur- 

 faces in Scotland striae crossing each other, and evidently 

 produced at different times by forces moving in different 

 directions. That the land-ice must have moved in the 

 direction of the slopes on which it rested, is self-evident; 

 and that the floating ice must have taken a southerly course, 

 is only what may have been expected, seeing that the cold 

 currents from the poles must ever be towards the warmer 

 and lighter waters of the equator. 



A third and important question is, whether this glaciation 

 of so large a portion, of the northern hemisphere was con- 

 temporaneous, or whether it passed gradually and succes- 

 sively over the areas of Europe, Asia, and America ? This 

 question, in fact, involves the cause of the glaciation, and 

 will be answered very mu(jh according to the views which 

 different theorists entertain. If we regard the ice-epoch as 

 brought about by external or astronomical causes, its con- 

 temporaneity is the most likely result ; but if we consider 

 it as arising from some peculiar distribution of sea and land, 

 and dependent on the earth's own physical relations, the 

 glaciation of Europe may have been separated by long ages 

 from that of America ; or, in other words, the ice-mantle 

 may have gradually crept from the one hemisphere to the 

 other, according as the set of polar currents was altered by 

 upheaval and depression of the land areas. In the mean 

 time, the general leaning seems to be towards the idea of 

 contemporaneity, though it must be confessed that a gradual 

 advance of the glaciation from area to area seems, in some 



