THE MECHANICS OF GLACIERS 



919 



in successive years ; and these positions, at any one time, will 

 correspond to those of successive annual strata.^ 



We readily see that the strata have a gentler slope than the 

 lines of flow in the reservoir, but a steeper slope in the dissipa- 



FiG. 2. Diagram of stratification [a), and lines of flow (b). Section and ground-plan. 



tor ; and that outcrops of strata can only occur below the neve- 

 line. 



The lower end of a new stratum is in the part of the glacier 

 where the horizontal motion is greatest, and it never sinks far 

 into the body of the dissipator, whereas, the upper end of the 

 stratum originates in a region of small horizontal motion and 

 later forms the lower layers of the glacier; the stratum, there- 

 fore, is stretched out and grows thinner on account of the differ- 

 ential motion, and also on account of the compression of the 



' Agassiz (Syst. Glac, pp. 273-276) very nearly reached this conception of the 

 disposition of strata and the direction of flow. Reverend O. Fisher (Phil. Mag., Lon- 

 don, 1879, Vol. VII, pp. 381-393) presents somewhat similar ideas in connection with 

 the stratification of Antartic ice. The theory presented above was developed before 

 I was familiar with the latter's work. 



