with Geognostical Observations, fyc. 137 



of psammite, to which formation it should doubtless be refer- 

 red. The slope of the mountain is on account of its declivity 

 so covered with debris that it is very difficult to penetrate to 

 the rock. Between these debris, beside the rock which forms 

 the summit of the mountain, and of which I have just spoken, 

 and the conglomerate also mentioned, pieces of serpentine and 

 schistoidal amphibole. 



The Youngouche itself, that is, the crest of this mountain, 

 is almost inaccessible. The ascent of it is dangerous ; the ir- 

 regular debris with which its flanks are covered slide beneath 

 the feet, and tumble into the abyss. The rock of which this 

 mountain is composed is a diorite, in which compact feldspar 

 predominates ; it is a grayish mass containing small needles of 

 amphibole, which sometimes unite into nodules and fill the in- 

 terior of small cavities. This grayish mass seems to be an in- 

 timate mixture of feldspar and amphibole ; the feldspar pre- 

 sents here and there points crystallized and whiter than the 

 rest, so that one is sometimes tempted to take this rock for a 

 porphyry. Microscopic points of sulphuret of iron are some- 

 times discovered in it. 



The conglomerates which I have described appear also in 

 various other points situated on the boundary of the trachytic 

 and secondary district, for example near the cascade of Tous- 

 loukchapap. The cascade itself is formed of a similar and 

 very large conglomerate, which rises perpendicularly above 

 the banks of the Malka to a considerable height. Enormous 

 blocks, which are no doubt detached from these rocks, obstruct 

 the bed of this river. On a slope less steep, upon which our 

 camp was established, we saw some rocks of serpentine and of 

 intermediary limestone penetrated by a stratum of the vege- 

 table soil which covered it. 



The stone bridge of Koubun is also formed of porphyroidal 

 diorite; the dioritic mass is of a pale green colour, and con- 

 tains white crystals of feldspar. These amphibolic rocks form 

 here, as they do every where in Caucasus, very rugged moun- 

 tains, bristled with aiguilles and crests, whose strange aspect 

 and sombre colour contrast singularly with the Hat but rug- 

 ged rocks of sandstone which follow in the order of their BU- 

 | hi position. t 



