ANCIENT GLACIERS. 



75 



of a drumlin would lead him to think that the mass was 

 entirely unstratified; but closer examination shows that 



Fig. 28.— Drumlins in the vicinity of Boston (Davis). 



there is a coarse stratification, but evidently not produced 

 by water-action. The accumulation has probably taken 

 place gradually by successive deposits underneath the 

 glacier itself. Professor William M. Davis has suggested 

 a plausible explanation which we will briefly state. 



The frequency with which drumlins are found to rest 

 upon a mass of projecting rock, the general co-ordination 

 of the direction of their axes with the direction of the 

 scratches upon the underlying rock, and the abundance 

 of scratched stones in them, all support the theory that 

 drumlins are formed underneath the ice-sheet, somewhat 

 in the way that islands and bars of silt are formed in the 

 delta of a great river. The movement of ice seems to 



