260 Wisco7ism Academy of Sciences, Arts, and Letters. 



So far, all is clear. So long as the glacier itself is present bear- 

 ing lateral moraines on its sides, medial moraines on its surface 

 and a ground moraine at its base, there is no room for confusion. 

 But this detrital material at length reaches the end of the glacier 

 and is deposited ; and here arises something of confusion in the 

 deposit itself, and something of confusion of ideas respecting it, or 

 at least, a want of accurate and precise use of terms. The phrase 

 terminal moraine is used to designate accumulations formed at the 

 extremity of the glacier. But, setting aside the terminal deposits 

 arising from the dropping of the lateral moraines, which remain 

 somewhat distinct, it is evident that the medial moraine will be 

 dropped upon the ground moraine at the foot of the glacier, and. 

 that this will occur under three conditions that ought to be distin- 

 guished. First, the foot of the glacier may be retreating, as is the 

 case at present, because the melting is more active than the onward 

 flow of the ice. Under these circumstances, the withdrawal of 

 the ice leaves the medial moraines as a ridge, or line of debris, 

 lying on the sheet-like ground moraine, and their relations remain 

 essentially the same as before, save that the glacier has vanished 

 from between them. In this instance the terms medial and 

 ground moraines may still be used appropriately to designate 

 them. 



Secondly, the foot of the glacier may be stationary, in which, 

 case the material of the ground moraine, pushed along beneath, 

 will accumulate at the glacier's margin in the form of a ridge, 

 and the medial moraines will pile up in heaps on this. To call 

 this simply a terminal moraine is not to speak very discriminately ; 

 for, in addition to the complexity of its own formation, it is liable 

 to be confused with that which arises under the third condition, 

 viz.: that in which the foot of the glacier is advancing. 



In this case the glacier is not only discharging material from its 

 surface and bearing it along its base, but it is plowing up that 

 previously deposited in its pathway.^ The result of this is the 

 formation of a ridge at the foot of the ice plow, as in the previous 

 case, but of more irregular character in respect, at once, to mate- 

 rial, structure, and surface configuration. This is a terminal 



' A portion is also overridden by the glacier. 



