STRATIFIED DRIFT 949 



indirectly responsible is stratified. That this should be so is 

 not strange when it is remembered that most of the ice was 

 ultimately converted into running water, just as the glaciers of 

 today are. The relatively small portion which disappeared by 

 evaporation was probably more than counterbalanced, at least 

 near the margin of the ice, by the rain which fell upon it. It 

 cannot be considered an exaggeration, therefore, to say that the 

 total amount of water which operated upon the drift, first and 

 last, was hardly less than the total amount of the ice itself. The 

 drift deposited by the marginal part of the ice was affected 

 during its deposition, not only by the water which arose from 

 the melting of the ice which did the depositing, but by much 

 water which arose from the melting of the ice far back from the 

 margin. The general mobility of the water, as contrasted with 

 ice, allowed it to concentrate its activities along those lines 

 which favored its motion, so that different portions of the drift 

 were not affected equally by the water of the melting ice. 



All in all it will be seen that the water must have been a 

 very important factor in the deposition of the drift, especially 

 near the margin of the ice. But the ice-sheet had a marginal, 

 belt throughout its whole history, and water must have been 

 active and effective along this belt, not only during the deca- 

 dence of the ice-sheet, but during its growth as well. It is fur- 

 ther to be noted that any region of drift stood good chance of 

 being operated upon by the water after the ice had departed 

 from it, so that in regions over which topography directed 

 drainage after the withdrawal of the ice, the water had the last 

 chance at the drift, and modified it in such a way and to such 

 an extent as circumstances permitted. 



Its origin. — There are various ways in which stratified drift 

 may arise in connection with glacier deposits. It may come 

 into existence by the operation of water alone ; or by the coop- 

 eration of ice and water. Where water alone was immediately 

 responsible for the deposition of stratified drift, the water con- 

 cerned may have owed its origin to the melting ice, or it may 

 have existed independently of the ice in the form of lakes or 



