526 THE JOURNAL OF GEOLOGY. 



over-riding or an over-sliding of the ice rather than of a pushing 

 or plowing up by the edge of the ice. It is my growing convic- 

 tion that this form of the terminal moraine is the predominant 

 one in the great American glacial field. I incline to the opinion 

 that the broad complex tracts of thickened drift that mark the 

 border of the ice sheet at several of its stages were chiefly formed 

 in this submarginal way, and that, while there is usually present 

 a constituent dropped from the surface of the ice and a con- 

 stituent formed by the mechanical thrust of the ice, the great 

 mass of these moraines, in general, accumulated by lodgment 

 under the border of the ice but near its edge. 



{b\ As only those ridges which have some measure of per- 

 sistency and which mark notable stages of the ice action should 

 be formally designated terminal moraines, it seems advisable to 

 recognize under a different head local ridges of till arranged 

 transversely to glacial movement. These are to be contrasted 

 with the drumlins which are elongated ridges of till whose axes 

 lie in the line of glacial movement. These transverse local 

 ridges are in some cases perhaps of the same nature as the sub- 

 marginal moraines except that the action was limited. But for 

 the greater part they may be presumed to have sprung either 

 from exceptional conditions of accumulation, which led to 

 exceptional deposition when the force of the ice was weakened, 

 or to exceptional conditions favorable to deposition, the con- 

 ditions in both cases determined by local agencies. They are 

 thus distinguished from the products of those general agencies 

 that produced the persistent submarginal moraines. 



2. Formations derived from material borne on the glaciers and 

 within them [but not at their basal contact) and deposited at their 

 margins or let directly down by their melting when stagnant. 



(i) Dump moraines [a variety of terminal moraines). — In 

 various well known ways a certain amount of material finds 

 lodgment on the surface of a glacier, and a certain additional 

 amount becomes incorporated within its body. Leaving out 

 of consideration such part of this as finds its way to the 

 bottom, both the englacial and superglacial material is carried 



