6 GLACIAL AND SURFACE GEOLOGY OF THE PACIFIC COAST. 



then, is very nearly the equivalent of the English word loam ; perhaps the best 

 way to define it would be to say that loam when developed enough to become 

 a formation of geological importance, and not a mere surface deposit, is loess. 



The chief difficulty in investigating the work of glaciers lies in the fact 

 that ice and water act together in almost all tliat is done in the way 

 of bringing about geological changes in and near the glacier. In regard 

 to a portion of this work it is impossible to say ice has done this, or ivatcr has 

 done that ; the two have acted toi!:ether in brino-ino: about the visible result. 

 xVnother consideration to be kept in mind is this, — that the glacier is not a 

 body of a certain fixed length. At the present time, and in former days, 

 glaciers increase and diminish in length and thickness, sometimes rapidly, at 

 other times slowly, and with repeated alternations of growth and diminution. 

 In these changes part of the previous work of the glacier is oblitei'ated, a 

 part obscured, and, on the whole, the difficulty of distinguishing what is 

 due exclusively to ice action is much increased. 



The simplest function of the glacier is that of carrying detritus. The 

 fragments detached from the walls of the valley through which the icy mass 

 passes fall upon the surface of the glaciei-, and resting upon it move down- 

 wards until they reach its terminus. The characteristic features of the 

 detrital material thus carried, and to which the name of " moraine " is applied, 

 are its angularity, and the absence of any regularity in the way in which it 

 lies, eitber while on the glacier itself or after having been delivered at the 

 terminus. Tlie material of the lateral moraine, or the detritus accumulated at 

 the edges of the glacier, when dumped at the end of the route becomes the 

 terminal moraine. A small portion of the detritus which falls on the glacier 

 falls through crevices or gets otherwise entangled in the ice, and is lost to the 

 moraine proper; but by f;ir the larger portion reaches the end of its course 

 very nearly in the same angular condition, and with the same heterogeneous 

 character, which it had at the beginning of its journey. The form and size 

 of the fragments of which the moraine is made up depend, of course, on the 

 character of the rock formations over which the glacier moves. The pieces 

 of rock rolled down from above will be transported with equal facility 

 whether — as is sometimes the case — of enormous size, or only in the form 

 of mere pebbles or sand. This is the criterion by which unaltered morainic 

 detritus may be recognized, and by which it may be distinguished from any 

 detrital deposits in the formation of which water has played a part. 



The character and position of the terminal moraine will vai y largely with 



