270 THE STORY OF THE EARTH AND MAN. 



they diverge into two schools. One of these, that 

 of the Glacier theorists, holds that the boulder clay 

 is the product of land-ice; and this requires the 

 supposition that at the time when it was deposited 

 the whole of our continents north of 40° or 50° was 

 in the condition of Greenland at present. This is, 

 however, a hypothesis so inconvenient, not to say 

 improbable, that many hesitate to accept it, and 

 prefer to believe tbat in the so-called Glacial period 

 the land was submerged, and that icebergs then as 

 now drifted from the north in obedience to the 

 Arctic currents, and produced the effects observed. 

 It would be tedious to go into all the arguments of 

 the advocates of glaciers and icebergs, and I shall 

 not attempt this, more especially as the only way to 

 decide the question is to observe carefully the facts 

 in every particular locality, and inquire as to the 

 conclusions fairly deducible. With the view of aiding 

 such a solution, however, I may state a few general 

 principles applicable to the appearances observed. 

 We may then suppose that boulder clay may be 

 formed in three ways. (1) It may be deposited on 

 land, as what is called the bottom moraine of a land 

 glacier. (2) It may be deposited in the sea when 

 such a glacier ends on the coast. (3) It may be 

 deposited by the melting or grounding on muddy 

 bottoms of the iceberg masses floated off from the 

 end of such a glacier. It is altogether likely, from 

 the observations recently made in Greenland, that in 

 that country such a deposit is being formed in all 



