ox THE VARIOLITIC ROCKS OF MONT GENKVRE. 299 



III, General Features of the Surface. 



The area occupied by the rocks studied in this paper coniprises 

 some sixteen square kilometres immediately to the south of the 

 highroad from ^lont Genevre to Clavieres. By " Mont Genevre " 

 we indicate the village of that name, at the summit of the well- 

 known pass, since the mountain or mountain-group once so desig- 

 nated is now known under other names. Our authorities in nomen- 

 clature have been the map on the scale of 1 : 80,000, published by 

 the French Depot de la Guerre, and revised to 1887 (sheet 189), and 

 that of the Italian Survey, 1 : 50,000, sheet 66, division 1, made by 

 the Istituto topografico militare in 1880. 



Three valleys open on the south side of the highroad at a level of 

 1800 metres, rising towards a line of hills that runs east and west, 

 beyond which, again, the ground descends rapidly to the valley of the 

 Cerveyrette, or Ccrvieres. The westernmost of these is the Gondran 

 Valleij, in which the upper Durance rises ; the floor is grassy, and 

 covered with pine-woods at the lower end, the stream ramifying 

 considerably in the more barren upland known as the Pros du 

 Gondran. On the west rise the grassy Cime du Gondran and the 

 sheer crags of Mont Janus (2514 metres), formerly spelled Juan, 

 Jouan, or Joux, and also styled sometimes Mt. Genevre. On the 

 east, above an intermediate platform used as cow-pasture, lie the 

 rocky ridge and taluses that run north-west for 1| kilometre from 

 Le Chenaillet. This peak, the highest point in the area (2634 

 metres, or 8642 feet), occupies, in fact, the south-cast angle of the 

 bounding wall, and sends out an important spur towards the Coi du 

 Gondran on the south. This col has an altitude of 2350 metres, 

 lying between the Cime du Gondran and Le Chenaillet. 



The second and central valley, which we term for convenience the 

 Chenaillet Valley, is bounded on the west by the steeper and more 

 rugged face of the Chenaillet ridge and, further to the north, by a 

 long tir-clad promontory, the end of which is surmounted by pale 

 limestone cliffs. On the south is an extremely picturesque col (2500 

 metres) which we hero terra the Col du Chenaillet, following the 

 system adopted in the Gondran Valley. On the east a series of 

 pinn.icled crags, reminding one of the north of Skye, leads up to 

 Mont La Plane ; the valley-floor, at first undulating and containing 

 several little lakes, falls rapidly on the right, the descent from the 

 col being over terraced clifl's until the stream is encountered, 

 running in a deeply-cut gorge. Above this gorge, on the east or 

 right hand, the slopes are formed of steep taluses, with a smooth 

 slate-blue exposure of serpentine ; on the west rise the walls of 

 rock th;it mark off the upper division of the valley. 



This upper or western division, into which one looks from Le 

 Chenaillet, falls much more gradually ; it contains no stream in 

 ordinary weather, and the cattle-track from the col descends along 

 it over glaciated bosses of gabbro until it reaches a smooth grassy 

 upland, from which one may cross to the Durance. We are here, 

 in fact, on the watershed between that stream and the Piccola Dora, 

 the waters of which fall into the Adriatic. 



