386 Bemarks on Glaciers. 



fragments, by protecting the part of the ice which they cover 

 from the action of the sun's rays and from rain, and also 

 from eA^aporation (which is often considerable, being occa- 

 sioned by warm or dry ^vinds), become, by the sinking of 

 the rest of the surface, gradually insulated on the summit 

 of a large pedestal or pillar of ice. This support, suffering 

 in its turn from the action of the same agents, soon gives 

 way ; the block rolls down, and forms another pyramid at 

 some distance. It is these that are called the tables des 

 glaciers, of which fine examples are afforded by the glaciers 

 of the Aar. If these fragments do not exceed an inch in 

 diameter, a phenomenon of a different description takes place. 

 Absorbing the solar rays, by their property as opaque bodies, 

 more rapidly than the ice, their entu'e mass (not the surface 

 merely, as in large blocks) becomes raised to a high tempe- 

 rature. Instead, therefore, of pi'otecting the ice beneath 

 them, they cause it to melt, and form holes which often 

 penetrate to a great depth ; they even pierce the glacier 

 from one side to the other ; for as long as a constant cause of 

 heat remains at the upper orifice, the water which fills them 

 is warmed above zero, then descends by virtue of its maximum 

 of density to the inferior beds, where it continues to perfo- 

 rate the ice by slowly melting it. When we add to these 

 phenomena the small currents of water running in every di- 

 rection, uniting into torrents, and throwing themselves in 

 cascades into the larger crevices which open or close by turns, 

 we shall be enabled to form an idea of the perpetual move- 

 ment going forward of the surface of a glacier. 



These blocks, scattered over the glacier, thus move along 

 with it, and at last reaching its edges, and being continually 

 thrown off, they accumulate and form masses of debris more 

 or less considerable, which are named moraines among the 

 Alps. These moraines are either lateral, disposed along the 

 glacier parallel to its sides ; or terminal, bounding its lower 

 extremity, and usually describing a semicircle ; or finally, me- 

 dian, forming long tracks on the surface of the interior of the 

 glacier itself. These latter are occasioned by a union of the 

 two lateral moraines of two glaciers descending two different 

 gorges, and uniting in the same valley. The two glaciers 



