62 DYNAMICAL GEOLOGY. 



currents set down blocks of stone in secure positions ; 

 while glaciers, in their slow melting, often leave them 



FIG. 30. Glaciated surface with perched bowlders. (After Geikie.) 



perched in insecure positions, and even sometimes as rock- 

 ing-stones. 



Deposit. Materials deposited by water are always 

 neatly sorted and stratified ; the materials deposited by 

 glaciers in terminal moraines are a confused heap of 

 fragments of all sizes, from fine earth to great blocks of 

 stone, dumped together without sorting. This heap con- 

 sists of two parts : the one contributed from above, the 

 other pushed out from below Aground moraine) ; the one 

 consists of loose earth and angular fragments, the other 

 of compact clay and rounded, striated fragments. Both 

 are wholly unstratified. 



Evidences of Former Extension of Glaciers. 

 The characteristic signs of glaciers, therefore, are smooth, 

 scored, moutonneed surfaces of rocks, large angular perched 



