Capt. Koschkull on the Caucasus, 219 
the central part of the principal chain where they form the ser- 
rated crest. The same rocks are also found in the Little Cau- 
casus, but not in great force. From the want of fossils, it is 
impossible to say whether these metamorphic slates belong to 
the Liassic formation or one still more ancient. 
Granite and gneiss are found upon the northern slope of the 
principal chain between Elbruz and Kazbek, in the valleys of 
the tributaries of the Terek. Over all this region the granite 
occupies the lowest place of all the rocks visible, and, judgin 
from the observations already made, it would seem that the 
granite masses in the region indicated the base of the principal 
mountain chain, associated with which are pyroxenic and tra- 
chytic rocks, which have been the active agents in the elevation 
of sag eeacphio rocks. 
e southern slo nite appears at one point in t 
chain of Rarthiodmeritis; aA ree also occupies the lowest 
positio 
position, 
The pyroxenic rocks, as melaphyre, pyroxenite, porphyry, 
basalt, and all the varieties of feldspathic porphyry, make their 
ippearance in the different parts of the principal chain of the 
ucasus, These rocks are not only the agents of elevation of 
the main chain, but they also form the most elevated summits 
between Fischt and Teboulos-mtha. 
At the northwest of Fischt, in Daghestan, all the igneous 
Tocks are covered by sedimentary deposits of enormous thick- 
hess, and such as have suffered great changes. In the south- 
east portion of the Little Caucasus, known under the name of 
: tains of Karabagh, amphibolic rocks, diorite and syen- 
ite, are found, but the principal agents in the formation of the 
Little Caucasus would seem to have been trachytic rocks, such 
48 trachytic, trachyte tufa, obsidian, and phonolite. In the 
Western of this chain, the rock and strata form great pla- 
teaus, w ich are sometimes deeply cut by fissures, in which 
