IGG Vrucccdiuifs uj' llic Jioj/at kiccieli/. 



appendage to thu main Alpine chain, which occupies a considerable 

 poition ot" the old province of Dauphine, and the modern depart- 

 ments of the Hantcs Alpes and Isa-c. It is bounded, roughly, by 

 the rivers Arc and Isere on the north, and by the Durance and the 

 Drac in other directions. Its nucleus is ess3ntially granitic, against 

 which sedimentary de})osits of limestone, of different ages, and espe- 

 '•■ially of lias and chalk, repose iri highly elevated or contorted strata ; 

 and it not unfrequently happens, that the dislocation of strata has 

 been so great, that the gneiss or granite rocks are superimposed upon 

 the secondary formations. 



The granitic mountains of Oisans, which are amongst the highest 

 of the second order of European chains, attain a greater elevation at 

 their culminating point, the Mont Pelvoux, than any of the Alps 

 between Mont Blanc and the Mediterranean. Even Mont Iseran 

 anl Monte Viso are surpassed in height by this sunniiit, which 

 measures 13,4G8 English feet. The ravines by which the chain is 

 intersected have a corresponding depth and ruggedness, so that the 

 cols, or passages from one valley to another, are generally covered 

 with pprpetual ice and snow, and present, besides, more continuous 

 and inaccessible precipices than are common in any part of Switzer- 

 land. The author shortly described several journeys made through 

 the central part of this district, in which it became necessary to 

 cross cols of above 10,000 feet in height, from whence alone an in- 

 timate knowledge of the structure of these mountains can be ob- 

 tained. 



Guided by the interesting memoir of M. Elie de Beaumont, on 

 the geology of the Montiigncs cV O'lsam-- , and by the admirable map 

 of Bourcet, he was enabled, in a great many particulars, to verify 

 the observations of the first named distinguishod geologist, especially 

 as refers to the phenomena visible at the contract of the calcareous 

 and granitic rocks, which left no doubt on the author's mind that 

 the superposition of the latter to the former is undeniably true. No 

 more can it be doubted, that, as M. E. de Beaumont affirms, we 

 have here evidence of the extensive elevation of previously deposited 

 sedimentary rocks, probably by the appearance from below of the 

 granite itself. Professor Forbes feels some hesitation in admitting, 

 with M. de Beaumont, the crcUerlforui, nature of this elevation, as 

 indicated by a 'jnd-qud-vr.'^al dip of the stratified rocks round a cen- 

 tral point in the neighbourhood of the Mont Pelvoux, and by the 



