270 Dlslrlbiifion of Rock !^ in the Erra/ic Jicisiti of the Tthonc. 



which come from the highest summits of tlie Alps ; while, in 

 the latter, these same rocks are accompanied by a much 

 greater variety of rocks, which I call secondary, and which 

 generally proceed from a part of the mountains below the 

 elevated summits. We ought thence to infer, that the rocks 

 of the eastern part were detached when the highest summits 

 rose alone from the bosom of the ice, while the rocks of the 

 westei'n part have fallen on the glacier when the inferior 

 rocks were uncovered, and yielded their contingent of very 

 varied rocks. Xow, the whole mode of the deposition of the 

 erratic formation, and the angular blocks it contains, pre- 

 senting themselves like a phenomenon of continued retreat 

 since the period of the greatest extension of the diluvian ice, 

 it follows that the deposites of the eastern part of the basin 

 represent the beginning, those of the western part the end, 

 of this long erratic period. 



Conclusions. — The facts which have been explained autho- 

 rise us, in my opinion, to affirm — 



\st. That the distribution of the species of rocks in the in- 

 terior of the basin of the Rhone is subject to a law. 



2d, That this law is, in all respects, conformable to that 

 which regulates the arrangement of moraines on an actual 

 glacier composed of many tributaries. 



3rf, That the great glacier which the extension and ar- 

 rangement of the Alpine debris, wdiich constitute the eiTatic 

 basin of the Rhone, presupposes, had its head in this prodi- 

 gious mass of the Pennine x\.lps and Mont Rosa, the most ele- 

 vated, most extensive, and richest in snowy peaks and pro- 

 found valleys — in a word, the most colossal of all those which 

 convey their tribute to the valley of the Rhone ; a vast re- 

 ceptacle of eternal snow and ice, which, even in the present 

 day, knows no rival among the Alps; insomuch that the 

 whole of Haut Yalais, on the one hand, and the valleys 

 which descend from Mont Blanc on the other, act simply as 

 its affluents. 



Thus we explain the grouping of the species of rocks in 

 parallel and linear zones, their distribution in special locali- 

 ties, and their respective situation, always confoi-mable to 

 the position of the valleys from which they have issued. 



