258 M. A. Guyot on the Distnhutlon of Tiocka 



They ascend very liigli on the chains of the Chabla'ia, with- 

 out, however, attaining the lieight of the granites, but leav- 

 ing below them the arkesines, which occupy chiefly the foot 

 of these heights. They still appear in blocks of many metres 

 on Mont (le Sion, Above the country of Gex, on the con- 

 fines of the Vaudois and Neuchatelese Jura, on the Suchet 

 and Chasseron, they reappear more frequently and in large 

 blocks. But more to the east the blocks ai'e smaller and 

 less numerous, and more talcose varieties, in which all gra- 

 nulation gradually disappears, become substituted for the 

 true granular chlorites. 



The chlcriteous gneiss, although abundant, rax'ely forms 

 large blocks; its presence is more intimately connected with 

 tliat of arkesine ; and we may consider what we are about to 

 state as to the distribution of the latter rock, as applicable to 

 it also. 



The arkesine, with its analogues, is the most widely spread 

 of these three rocks ; its true domain is the south-west part 

 of the basin. We find it along the Savoyard side of the Lake 

 of Geneva ; it forms the great majority of the blocks on 

 Mont de Sion, Vouaehe, and the country of Gex. More to the 

 east, it accompanies the granites of Jura, in blocks still nu- 

 merous, but of much smaller size. In the plain we find it 

 abundantly between Neuchatel, Fribourg, and Berne ; it forms, 

 almost by itself, some leagues from Soleure, the largest blocks 

 known, not only in the basin of the Rhone, but in all Switzer- 

 land, such as the great block of Stienhof, and, quite near to 

 that, those of Steinberg. 



Thus, then, the Pennine rocks are found almost through- 

 out the whole extent of the basin. No region is exempt, 

 unless it be the right side of the valley of the Rhone, and be- 

 yond the Alps, the countries situate at the foot of the moun- 

 tains of Gruyere. Everywhere the chlorites abound, particu- 

 larly on the left bank of the Lake of Geneva, while the arke- 

 sines, along with the chloriteous gneiss, prevail in the central 

 portion of the basin, especially, on the one hand, on Mont 

 de Sion and in the country of Gex, and, on the other, at the 

 cxtremityof the north-east, in the plain to the south of Soleure. 

 The respective situation of the regions where the one or other 



