the Revolutions 'which have taken place on the Globe. 257 



consequence of the crossing of these two systems of furrows 

 and ridges, the French Alps form an elbow near the Mont 

 Blanc, and after having followed a direction from E. ^° N.E. 

 to W. ^° S.W. li-om Austria to the Valais, they suddenly 

 turn to fall into a line from N.N.E. to S.S.W. If there was 

 only a simple curve m a single chain of mountains which 

 merely formed an arch, we should find the direction of the 

 beds to bend and pass from the direction of one of the sy- 

 stems to that of the other. We however observe, that the 

 direction of the beds and crests distinctly belong either to one 

 or to the other, and that the two systems penetrate each other, 

 as we should conceive they must do if they are the produc- 

 tions of two entirely distinct phaenomena. 



In the Western Alps, that is to say, to the westward of the 

 St. Gothai-d, and particularly in the mountains of Savoy and 

 Dauphiny, the greater part of the dislocations are referrible 

 to two systems of ridges, the mean direction of which is N.N.E. 

 and S.S.W., or more exactly N. 26° E., and S. 26° W. The 

 constant direction of the beds in these mountains has long 

 since been remarked by De Saussure, and more recently by 

 M. Brochant; and they with reason concluded, that in all those 

 parts where this direction predominated, the beds were thrown 

 up by a single operation of nature. 



It is easy to determine the geological date of this event; for 

 we have only to examine what are the formations which have 

 been disturbed, and what the deposits which extend horizon- 

 tally on the edges of the dislocated and more ancient strata. 



In the interior of that system of ridges of which the Western 

 Alps are principally composed, we do not find beds more re- 

 cent than the chalk, because these ridges have been formed on 

 a surface previously made mountainous, at the epoch of the 

 systems of Mont Viso and the Pyrenees. But on the skirts, 

 as also at the two extremities of the space occupied by the 

 ridges to which the character of the Western Alps is due, we 

 find that the dislocations which have produced the ridges are 

 carried into the most recent tertiary deposits, as well as into 

 the secondary rocks which support them : whence it follows, 

 that the elevation of the beds in the system of the Western 

 Alps took place after the deposit of those recent tertiary beds, 

 named shelly molasse {mollasse coquilliere), beds contempo- 

 raneous with the JfMims of Touraine. 



XII. System of the principal Chain of the Alps {from the 

 Valais to Austria), comprising also the Chains of the Ventoux, 

 the Libcron, and the St. Baume {P70vence). — The valleys of 

 the Isere, the Rhone, the Saone, and the Durance, present 

 two very distinct detrital and transported formations, between 



N.S. Vol. 10. No. 58. Oct. 1831. 2 L which 



