GEOLOGICAL OBSERVATIONS IN FRANCE, &C. 273 



separated from it only by the mountains Saleve, Sion, and 

 Vouache, has for its limits to the south a chain of moun- 

 tains in the same line as mount Brison, and the direction of 

 which is parallel to that of the central chain. The course 

 of the Arve, "and the low mountains that skirt the western 

 shore of the lake of Annecy, are its boundaries to the north- 

 east and south-west. 



Mr. Saussure has described only the mountains on the Southern 

 north of this valley. The chain on the south, taken toge- * 



ther, is at least 15 miles long-. Its greatest height, like that 

 of the Jura, is to the south-west. One mountain there, la La Toumette. 

 Toumette, rises 040 toises above its base. The precipices 

 of this chain look from the Alps, that is to say, the strata 

 slope toward them. The limestone that composes them is Silex inter-- 

 compact, including great numbers of imbedded flints, and s P ersed m 

 not unfrequently we meet with calcareous rocks, the tops of 

 which are completely capped with silex. 



Though the mountains that form this chain are all con- 

 nected together, except that the continuity is occasionally 

 interrupted by a transverse valley, they have almost as 

 many different names, as there are parishes at their feet. 

 The strata are much more regular in the north-east part of 

 the chains, than in the south-west. Thus the mountains of 

 St. Laurence display horizontal banks, much resembling 

 those of mount Saleve ; while at Villaz and Dingy, where 

 the principal branch of the chain has a perceptible inflexion 

 to the south', the strata lose their uniform horizontality, and Variation in 

 this more and more as we approach Tournette, where we the strata. 

 "see some completely broken, others arched or raised upon 

 themselves; a character, as already observed, announcing 

 the vicinity of a transition chain. The back of this chain 

 toward the Alps falls into the valley of little Bornand, at the 

 bottom of which flows the river Borne. Over this river is a 

 bridge more than sixty feet high. 



The two principal summits of this chain are Pormonaz Pormonaz. 

 and Toumette. Pormonaz is nearly in the middle of the 

 chain, and rises 540 toises above its base. The first part of 

 the ascent is through a very thick wood, from which, after Thi k wood. 

 a journey of two hours and half, you enter into rich pas- p asl 

 tures, bounded on all sides, except to the north-east, by 



Vol. XIX— April, 1808. T cliffs 



