M. Renoir on the Traces of Ancient Glaciers, 81 



order of phenomena seems to have been repeated at the same 

 epoch over the whole surface of the earth : whence, then, could 

 all these immense currents be derived % 



The reasons we have stated, and others which we shall still 

 adduce, lead us almost irresistibly to regard the erratic blocks 

 which we meet with in the bottom and on the sides of the 

 small valleys of the district of Chartreuse, as having been de- 

 posited there by an immense glacier, which, in the last geo- 

 logical epoch, descended from the summit of the Alps and 

 filled the valley of Graisivaudan. In this country, accordingly, 

 the traces of ancient glaciers are numerous. We meet with 

 the remains of moraines, with their blocks, in almost all the 

 valleys ; at the outlet of that of Guier Mort, at Fourvoirie ; 

 along and to the north of the road from St Laurent-du-Pont 

 to Voreppe ; in the valley of the Romanche, near the inn of 

 the " Trois Dauphins," below which polished surfaces are to be 

 seen ; to the west of the road from Grenoble to La Mure ; in 

 the neighbourhood of the three Lakes, &c. But it was parti- 

 cularly when I left Grenoble to repair to Lyons, by Vienne, 

 at the outlet of the valley of the Isere between Moirans and 

 Rive, that I fell in with two lines of enormous moraines, whose 

 extent indicates that of the glaciers by the oscillations of 

 which they were formed. Beyond Rive, other remains in an 

 imperfect state of preservation appeared, but soon nothing 

 more was to be seen than an extensive plain of sand and rolled 

 pebbles, of the nature of the Alpine rocks. It may be ob- 

 served, that in proportion as we retire farther from the Alps, 

 the quartz-pebbles become more frequent, until they prevail 

 almost exclusively, as if this kind of rock had been more able 

 than the rest to resist the friction and other causes of destruc- 

 tion. It is not till much later, and when the melting of the 

 ice had carried back the limits of the glaciers as far as the 

 mountains, that the great rivers which flowed from them, and 

 of which those w^e now behold are only the remains, began to 

 mark out and fix their beds in these moveable deposits, taking 

 a&vantage of the kind of valleys which the moraines leave be- 

 tween them, or other accidents of the surface. We may men- 

 tion as an example the Isere, which, issuing from a fracture 

 in the calcareous mountains between Fourcy and Voreppe, 

 turns suddenly to the west, then to the south, in order to flow 

 through, in its course towards Saint Marcelin, the kind of void 



VOL, XXXI. NO. LXI.^JVLY 1841. F 



