The situations of the principal summits can be perceived at a glance on the accompanying map, which is a reproduction of a portion of sheet 189. The main ridge of the chain runs, at this part, nearly north and south. Roche Faurio, at the northern extreme, is 3716 mètres, or 12,192 feet, above the level of the sea. The lowest point between that mountain and the Ecrins (the Col des Ecrins) is 11,000 feet. The ridge again rises, and passes 13,000 feet in the neighbourhood of the Ecrins. The highest summit of that mountain (13,462 feet) is, however, placed a little to the east of and off the main ridge. It then again falls, and in the vicinity of the Col de la Tempe it is, perhaps, below 11,000 feet; but immediately to the south of the summit of that pass, there is upon the ridge a point which has been determined by the French surveyors to be 12,323 feet. This peak is without a name. The ridge continues to gain height as we come to the south, and culminates in the mountain which the French surveyors have called Sommet de l’Aile Froide. On the spot it is called, very commonly, the Aléfroide. There is some uncertainty respecting the elevation of this mountain. The Frenchmen give 3925 mètres (12,878) as its highest point, but Mr. Tuckett, who took a good theodolite to the top of Mont Pelvoux (which he agreed with his predecessors had an elevation of 12,973 feet), found that the summit of the Aléfroide was elevated above his station 4′; and as the distance between the two points was 12,467 feet, this would represent a difference in altitude of 5 mètres in favour of the Aléfroide. I saw this mountain from the summit of Mont Pelvoux in 1861, and was in doubt as to which of the two was the higher, and in 1864, from the summit of the Pointe des Ecrins (as will presently be related), it looked actually higher than Mont Pelvoux. I have therefore little doubt but that Mr. Tuckett is right in believing the Aléfroide to have an elevation of about 13,000 feet, instead of 12,878, as determined by the French surveyors. Mont Pelvoux is to the east of the Aléfroide and off the main ridge, and the Pic Sans Nom (12,845 feet) is placed between these two mountains. The latter is one of the grandest of the Dauphiné peaks, but it is shut in by the other mountains, and is seldom seen except from a distance, and then is usually confounded with the neighbouring summits. Its name has been accidentally omitted on the map, but its situation is represented by the large patch of rocks, nearly surrounded by glaciers, that is seen between the words Ailefroide and Mt. Pelvoux.