Geological Society. 



505 



the Rhone, the Arve, the Aar, &c. ; likewise in Scotland, near Inve- 

 rary, 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 Ken- 

 dal, as w ell as near Penrith and Shap. 



The common origin of moraines, and of accumulations of rounded 

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

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

 rounded under glaciers, or great masses of ice, and exposed by the 

 melting of the ice, and re-arranged by the water thus produced. 



The author then proceeds to describe the internal arrangement of 

 these 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, the largest blocks being 

 often in the upper part ; and where very large angvlar blocks occur, 

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

 in blocks of all dimensions and every form being 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 rounded on their edges. 



The striated and polished surfaces, so often observed on solid 

 rocks in situ, is 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 of water consist in sinuous 

 furrows on the softer portions of rocks ; not in even uniform polished 

 surfaces, such as those presented by the rocks under discussion, 

 and which are independent of the composition of the stone. This 

 view of the nature of these polished rocks is borne out by the effects 

 of existing glaciers, the rocks in contact with them having the angles 

 rounded off, and the surfaces polished, as well as striated. These 

 phenomena M. Agassiz has traced under the glacier of the Aar, and 

 he has observed them in the valley of the Rhone, and of Chamonix ; 

 also in Scotland, 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 striae, are their 

 diverging at the outlets of the valleys, and their being oblique, and 

 never horizontal on the flanks, which they would be were they due 

 to the agency of water. The cause of this obliquity the author as- 

 signs to the upward expansion of the ice, and the descending motion 

 of the glacier. 



The most remarkable striated rocks in the Alps are near Handeck, 

 and near the cascade of Pissevache ; and the best examples M. 

 Agassiz has seen in Scotland, are those of Ballahulish, and in Ireland 

 those of Virginia. 



If the analogy of the facts which he has observed in Scotland, 

 Ireland, and the north of England, with those in Switzerland, be 

 correct, then it must be admitted, M. Agassiz says, that not only 



