82 EMBOSSMENT. 



Some other cases of stria? in Vermont remain to be described, which we have been in 

 the habit of referring to ancient glaciers, in distinction from the drift agency. But these 

 will be better understood if we previously make a few remarks upon 



PLANISHING AND EMBOSSMENT. 



We have already stated that planishing or smoothing of the surface has taken place 

 where the rock is quite hard, or the materials quite fine. The hardness is also favorable 

 in general to the preservation of the rock. Hence quartz rock and silicious limestone 

 often exhibit a smoothness scarcely inferior to artificial polish. A level surface is perhaps 

 most favorable for the exhibition of this variety of the phenomena of abrasion. Yet it 

 is often shown very finely on embossed surfaces. In this variety there must be a 

 considerable inequality of surface, and it is the rounding of the angular protuberances 

 which constitutes the embossment. Consequently as it was done by some body urged 

 over the surface, one side of the elevations would be rounded more than the others. This 

 struck side is called in Sweden the Stoss side, and its opposite in English the Lee side, or 

 the sheltered side, which rarely shows any abrasion. This distinction is very important, 

 for it enables us to determine the direction of the abrading force. 



Most frequently the embossed surfaces are striated. Yet when the striae are all obliter- 

 ated by disintegration, the rounded form of the bosses and the distinction between the 

 stoss and lee sides remains ; so that this variety of the drift agency is the most perma- 

 nent of its mementos. It occurs also on the grandest scale : for often a large mountain 

 constitutes a single boss. Indeed most of the mountains in the northern parts of our 

 country owe the rounded form of their summits so different from those in the Alps, 

 for instance to this agency. 



STEIATION, PLANISHING, AND EMBOSSMENT BY ANCIENT GLACIEKS IN 



VEEMONT. 



Glaciers are vast rivers of ice, which, starting from the snow-capped summits of lofty 

 mountains, move slowly down the valleys as far as the heat of summer will permit them. 

 Though they rarely ever advance more than two feet a day, even in summer, yet their 

 great thickness and the weight of the superincumbent snow cause them to grate hard 

 upon the rocky surface beneath; and they do, in fact, produce all the phenomena of stria- 

 tion, planishing, and embossment, which have resulted from drift. Nor can the two 

 classes of phenomena be distinguished by anything in their appearance. But glaciers 

 also crowd along huge masses of detritus, from the largest bowlders down to impalpable 

 powder, which are called Moraines. The moraine in front of the glacier often nearly fills 

 the valley to the height of 100 or 200 feet, and the lateral moraines are scattered along 

 the sides of the valley. 



In many parts of ^Europe, as Wales and Scotland, those stria3 and moraines are found 

 in such circumstances as to indicate the former presence of glaciers where they have not 

 existed within historic times. It has long been an interesting inquiry whether any similar 

 markings exist on any of the mountains of this country. To the White Mountains we 



