The Annals and Magazine of Natural History. 449 



snow, and as all ice has previously been water, it is clear there 

 can be little of it in a solid form at great elevations. The blocks 

 and masses of rock that are detached from surrounding precipices 

 above, consequently sink through the mass to the bottom of the 

 snow. At lower elevations, the melting process during summer 

 is more active on the surface of the glacier, and the water per- 

 colates through the porous mass till it reaches the rocks on 

 which it rests. Here it is converted into ice, which by its expansive 

 property tends to detach and burst fragments from the rocky bed, 

 the ice, still acting as a wedge, thickens imperceptibly and forces 

 up the superincumbent mass, and with it the stones and gravel which 

 it had entangled at the bottom. When the heat of the sun during the 

 summer melts the upper layers of ice ; the masses thus detached are 

 precipitated from the glacier, forming what are called morains, or 

 accumulations of loose stones which skirt the glaciers below. 



Thus glaciers have been found to produce certain remarkable 

 effects, not only on the acclivities which they occupy, but also on the 

 character of the plains below, and these effects in both cases are so 

 peculiar as scarcely to be mistaken. Besides horizontal terraces and 

 morains, glaciers during their gradual descent occasionally produce 

 polished grooves in the rocks over which they slide. These are 

 described by M. Agassiz as highly polished lines passing in the 

 direction in which the glacier moves, and are produced by grains 

 of quartz and fragments of rocks moved by the action of the 

 ice down the surface of the rocks. These grooves are fresh and 

 sharp beneath existing glaciers, but less distinct on surfaces that have 

 been left for some time exposed to atmospheric action. Having 

 thus established the peculiar modifications of the surface produced by 

 glaciers, M. Agassiz was surprised to find traces of their existence 

 in climates and altitudes where such causes could little be 

 expected to have operated. Thus in several parts of Scotland, 

 Ireland, England, and Wales, M. Agassiz has discovered effects 

 which can only be referred to these causes, and which it is ex- 

 pected will clear up much of the mystery connected with erratic 

 blocks. The subject is one of much interest, and as we think it is 

 capable of being elucidated and matured by observations in the 

 Himalaya, we shall probably quote M. Agassiz's views in detail, on 

 some future occasion, when we are less pressed for space than 



