266 M. A. Guyot oii, the Distribution of Rocks 



Here, again, we observe the rocks succeed each other in tlie 

 same order as in the preceding section ; and this order is that 

 in which these same rocks have advanced from below up- 

 wards into the principal valley. First, tlie granites of the 

 left bank and of the lower part of the valley ; then the 

 chlorites of Bagnes, the arkesines and chloriteous gneiss 

 of Val d'Erin, the serpentines of Mont Rosa, and the 

 euphotides of Saas, and lastly, confusedly mixed, the rocks 

 of the right bank with the granites of Mont Blanc, which 

 belong, as we shall afterwards see, to the effusion of the 

 eastern part. 



It is therefore correct to affirm, as I did at the outset, that 

 the disti'ibution of the species of erratic rocks is subject to 

 a laAV, according to which the transported debris of roclvs of 

 the same species preserve in the plain a determinate position, 

 which is assigned to them by the respective situation of the 

 valleys from which they issue. The rocks which proceed from 

 the lateral valleys, nearest the opening of the principal valley, 

 keep the margin on one side or the other ; such as proceed 

 from the most remote tributai'ies remain in the centre. 



This law of distribution I have also observed to hold true 

 in the basin of the Rhine, and more distinctly still in that of 

 the Reuss, which is more simple than the two others ; but a 

 circumstance which is peculiar to the basin of the Rhone is the 

 double divex'gency of which I have spoken. We may perceive 

 that each of the two branches, eastern and western, i-epre- 

 sent, in their order, the rocks of the valley of the Rhone 

 considered collectively. Now this disposition compels us to 

 admit two periods of divei'gency. During the first, the issue 

 took place only on the north-east side, that is to say, on 

 the most open side of the great valley lying between the 

 Alps and the Jura. In a second epoch, the effusion must 

 have taken place by the much narrower basin of Leman, to- 

 wai'ds the plain of Geneva and the country of Gex. 



The analogy between this distribution and that of the mo- 

 raines of a glacier, is evident, and must strike every one. 

 The arrangement in linear series, which the superficial mo- 

 raines affect, the imiformity of the respective situations they 

 preserve, in spite uf all the angles and contours of the val- 



