with Geognostkal Observations, Sfc. 139 



top of Elbrouz is entirely covered with snow, which is easily 

 kept on its sides, which are generally not very steep. 



When we arrive near the middle of its declivity, we perceive 

 that the lowest trachytic crests which surround it range them- 

 selves around it, and encircle its base. Elbrouz itself seems 

 to rise in the middle of a cavity, whose margin is formed by 

 the trachytic crests I have mentioned- In looking northward 

 we see the Kinjal, the Inal, and the Bermamuc, present the 

 same arrangement. All these mountains exhibit precipices 

 turned towards Elbrouz, or towards the central chain ; while 

 to the north they slope insensibly, and form the immense pla- 

 teau of which we have already spoken. 



The trachyte, (i. e. all the porphyries which envelope in their 

 mass crystals of vitreous feldspar,) which compose the sum- 

 mit of Elbrouz itself, holds a middle place between the resinite 

 feldspar and the obsidian porphyries. Its mass, which enve- 

 lopes many white crystals of glassy feldspar of an average dia- 

 meter of two or three lines, is black and opaque, of a rough and 

 uneven fracture, and of a vitreous aspect. On the fissures 

 which traverse it in all directions, and which divide it into 

 masses of a form approaching to that of the parallelipiped, it 

 is coloured red, probably by the oxidation of the oxide of iron 

 which it contains. Small scales of black amphibole and of 

 black or bronzed mica are disseminated through the mass. 



The approaches of Elbrouz present the picture of destruc- 

 tion. Enormous blocks of the trachyte which I have describ- 

 ed are heaped one upon another. Their debris cover the bot- 

 tom of the excavations, and of the high valleys which sepa- 

 rate them. These debris often preserve, while decomposing, 

 their salient edges, and prevent the formation of vegetable soil. 

 Though traversed by a thousand brooks fed by the melting of 

 the snow, the ground is parched, and rolls down with a noise 

 beneath the feet of the traveller. The rocks which I collect- 

 ed during this ascent present different varieties of trachyte 

 and lavas ; they are disposed without order, and they obstruct 

 the beds of the rivers, particularly that of the Malka, from 

 which I have obtained a great number of them. 



Among these we particular]; distinguished B lava of very 

 porous and grey feldspar, which envelopes while crystals ol 



