676 DYNAMICAL GEOLOGY. 



moraines may be seen on the distant part of the glacier. In fig. 

 949, representing a section of the Bois Glacier near Trelaporte, 

 there are six distinct moraines. 



Toward the lower extremity of a glacier (as shown in fig. 950, 

 from the lower part of the Bois Glacier) the several moraines usually 

 lose their distinctness through the melting of the ice ; for this brings 

 the stones and earth that were distributed at different depths to 

 one level, and thus produces a coalescence of the whole over the 

 surface. 



The stones are both angular and rounded, the former far the 

 more abundant. Many are of great magnitude. One is men- 

 tioned containing over 200,000 cubic feet, or equal in size to a build- 

 ing 100 feet long, 50 wide, and 40 high. 



At the glacier of the Aar, the central moraine is raised 100 to 140 

 feet above the general surface either side ; but this is partly owing 

 to the pressing up of the ice itself by the mutual pushing of the 

 two combined glaciers of which it is made. The breadth where 

 narrowest is 250 feet ; and from this it increases to 750 feet half- 

 way to the termination of the glacier, and to treble this below. 



The final melting of a glacier leaves vast piles of unstratified 

 stones and earth along its sides, toward and about its lower ex- 

 tremity. The stream which proceeds from the glacier works over 

 all that comes within its reach, carrying it onward down the valley, 

 and making deposits on its banks which are usually more or less 

 perfectly stratified. 



2. Erosion. — (1.) The movement of a glacier is attended with so 

 much wrenching of the ice, that the blocks generally have their 

 angles more or less blunted by mutual attrition, and many of the 

 stones are rounded. 



(2.) As the glacier has its sides and bottom here and there set 

 with stones of large and small size, it is a tool of vast power as 

 well as magnitude, scratching, ploughing, and planing the rocks 

 against or over which it moves.' Besides this, it pushes along gravel 

 and stones between itself and the rocks, with the same kind of 

 effect. The rocky cliffs and ledges in the vicinity of the glaciers 

 are in many places furrowed, planed, and rounded over their whole 

 exposed surface from this agency. The furrowings or gougings 

 have a common direction ; but there are sometimes two or more 

 directions, indicating glacier-movements of different periods. 



(3.) The stones which have produced the furrowing are some- 

 times scratched themselves. 



Other facts connected with this subject are mentioned on page 

 535. See also the works of Agassiz, Forbes, and Tyndall. 



