572 Geological Societj/: — Prof. Agassiz o?i Glaciers, 



ivcly abandoned by them in their retreat. The longitudinal mo- 

 raines differ from glacier-detritus remodelled or spread out by water, 

 in being disposed in ridges with a double talus, one flank of which is 

 presented to the glacier, and the other to the side of the valley ; and 

 their continuity and parallelism at the same height easily distinguish 

 them from the debris disposed along the bottoms of valleys by cur- 

 rents. They occur on the flanks of all glaciers, but they have been 

 also observed by M. Agassiz where no glaciers exist, as in the val- 

 leys of the Rhone, the Arve, the Aar, &c. ; likewise in Scotland, near 

 Inverary, at Muc Airn, at the outlet of Loch Traig, at Strankaer, 

 and on the borders of the bay of Beauley ; in Ireland to the south- 

 east of Dublin, and near Enniskillen ; and in England in the valley 

 of Kendal, as well as near Penrith and Shap. 



The common origin of moraines, and of accumulations of rounded 

 pebbles and of blocks, M. Agassiz says, cannot be doubted. The 

 former are simple ridges formed on glaciers ; the latter, materials 

 rounded and polished under glaciers, or great masses of ice, and ex- 

 posed by the melting of the ice, and re-disposed by the water thus 

 produced. 



The author next describes the differences in the internal arrange- 

 ment of the various accumulations. In the stratified deposits the 

 materials are comparatively much smaller than in glacier-detritus ; 

 the pebbles also are elongated, and fine gravel and mud ordinarily 

 form the upper beds. On the contrary, in the detritus of glaciers 

 large and small materials are associated without order, tlie largest 

 blocks being often in the upper part ; and where very large angular 

 blocks occur, they rest on the surface. In moraines there is a further 

 distinction, blocks of all dimensions and every form are intermingled ; 

 and this difference, he says, is easily understood, by recollecting that 

 moraines are composed of the angular blocks which fall on the sur- 

 face of the glacier, as well as of pebbles with rounded edges. 



The striated and polished surfaces, so often observed on solid 

 rocks in situ, are next described by M. Agassiz. Without denying 

 absolutely the power of water to produce such effects, he says that 

 he has sought for them in vain on the borders of rivers and lakes, 

 and on sea-coasts ; and that the effects produced by water are sinuous 

 furrows proportioned to the hardness of the rocks ; not even uniform 

 polished surfaces, such as those presented by the rocks under dis- 

 cussion, and which are independent of the composition of the stone ; 

 moreover wherever the moveable materials which are pressed by the 

 ice on rocks in sihi are the hardest, there occur, independent of the 

 polish, striae more or less parallel, and in the general direction of 

 the movement of the glaciers. Thus in the neighbourhood of gla- 

 ciers are found those rounded bosses which Saussure distinguishes 

 by the name of " roches moutonnes." These phaenomena M. Agas- 

 siz has traced under the glacier of the Aar, and he has observed 

 them in the valley of the Rhone, and of Chamounix ; also in Scot- 

 land, on the banks of Loch Awe and Loch Leven ; and he says they 

 are very remarkable in the environs of Kendal. 



The most striking points in the distribution of the strise, are their 



