M. A. Guyot on the Erratic Basin of the Bhine. 23 



limestone debris, the number of which, in this place, greatly 

 exceeds that of the crystalline rocks of the valley of the Rhine. 

 An important remark is this, that, from the moment when 

 these limestones come in contact with the rocks of the Rhine, 

 the angular blocks disappear, but thenimierous rolled blocks 

 which replace them are almost all strongly furrowed and 

 striated. This circumstance seems to indicate that the cal- 

 careous blocks had already taken possession of these coun- 

 tries when the erratic rocks of the Rhine came thither, and 

 that it is to the agent which transported them to these places 

 that we must ascribe this change in their manner of exist- 

 ence. 



Tlie existence of this new erratic region proves that, from 

 the height of these calcareous summits also, has descended 

 an alluvium, whose characters are absolutely the same as 

 those of the erratic basins with primitive rocks, and which 

 has no doubt been dispersed by causes altogether ana- 

 logous. The insxilarity of this erratic region in the middle 

 of the basin of the Rhine, its distance from the central chains 

 of the Alps, and the calcareous nature of its debris, are a 

 proof that the erratic phenomenon is not necessarily con- 

 nected with the presence of the crystalline rocks, as has been 

 alleged, nor with the greater or less depth to which the val- 

 leys from which these debris descend penetrate into the cen- 

 tral chains ; but that it rather depends on the conditions of 

 height wliich may be met with beyond the principal mass of 

 the Alps, as well as on their summit. Every orographic mass 

 sufficiently elevated to become, if its structure admit of it, 

 a centre of glaciers, may likewise become the centre and 

 point of departure of a particular erratic formation. It would 

 seem that facts of this nature are destined to restrict greatly 

 the field of hypotheses by means of which we may give an 

 explanation of the erratic phenomena. 



The distribution of the species of rocks in the erratic basin 

 of the Rhine, without being so complicated as that of the 

 species of the basin of the Rhone, is not less interesting from 

 its regularity. It is subject to the same law which we have 

 ascertained to operate in the other basins. 



Among the various rocks which have descended from the 



