358 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [April 5, 



masses of ice floating about in rivers, or on the surface of lakes, in the 

 transport of great angular rocks. Even in the present time large 

 rocks are transported on the shores of the Arctic seas from one point 

 to another ; and the great masses of fine granite blocks vphich cover 

 the plains of northern Germany, up to the foot of the Harz and 

 the Silesian mountains, came very probably on similar icebergs and 

 ice-floes from the Scandinavian peninsula. 



On Polished Rock-Surfaces. 



In relation to the erratic phsenomena and their connexion vidth an- 

 cient glaciers, I propose to add a few remarks upon the polished and 

 striated rocks, which have been considered, I think in some instances 

 with too little hesitation, as general evidences of the presence of 

 ancient glaciers. 



There can be no doubt whatever, that the glaciers have the faculty 

 of extensively producing by their movement polished and striated 

 rock-surfaces on their borders. These interesting phaenomena can 

 be traced sometimes at very great distances from the present glaciers. 

 They are seen very well developed in the environs of the glaciers of 

 Macugnaga and of Gorner, especially on the lower termination of the 

 Gorner glacier*. 



But there are still many other agencies which can produce similar 

 phsenomena in a very deceptive way. I will not dwell on the polished 

 and striated rocks produced by land-slips, so very common in the 

 Alps ; or on the striae resulting from a small amount of sliding of 

 sedimentary strata one along the other, which I clearly observed in 

 several quarries : but I will merely call the attention of the Society 

 to the fact, that the gneiss as well as the granite of the Alps very 

 often shows a concentric exfoliation ; and that all these concentric 

 laminae, having very difl'erent dimensions and very various degrees of 

 curvature, ofi"er on their surfaces a fine polish and fine parallel striae, 

 which are not limited to the superficial surface, but are repeated on 

 all the laminae in the interior of the rock. 



It is quite evident that in vSuch a case the polish and the striae 

 of the rocks cannot be attributed to the action of glaciers, which could 

 but have afi'ected the very surface of the mountains, never the interior 

 laminae of the rock. It seems that these phsenomena are here inti- 

 mately connected with the process of the concentric exfoliation itself; 

 and that a limited sliding and displacement of the different folia or 

 laminae have taken place, which produced the fine parallel striae and 

 scratches so generally observed in these instances. 



Leopold von Buchf was the first to show the importance of these 

 polished concentric laminae in Sweden and in the Alps : guided by his 

 directions, I have endeavoured more fulh'towork out the subject in the 

 Alps, and to represent some of the most characteristic forms of these 

 concentric exfoliations oa the three plates now exhibited to the Society. 



* Lithographic ilhistratious of these phaBiiomena (prepared for the Author's 

 larger Memoir) were laid before the Meeting. 



t Ueber Granit und Gneiss ; Abhandluugen der Berliner Akademie fiir 1842. 



