KIRGHIS FRONTIER.— MAGNITNAYA TO ORSK. 
445 
prevalent variety of which is of a reddish colour, with large white crystals of fel- 
spar, and a little quartz. Another variety, occasionally columnar, like some of the 
porphyries of the Isle of Arran, has a dark grey compact base, with crystals of light 
colour ; and a third has a light grey base, with crystals of pink felspar. As in 
many other parts of the world, where such bosses and ribs of porphyry are flanked 
by schists, the latter at the points of contact are in a jaspideous condition. A 
little to the north-east of the station of Magnitnaya, and on the opposite hank of 
the river Ural, the chain is subtended by a parallel ridge containing magnetic iron 
ore, and called theUla Utasse-tau, which is also associated with porphyry . This 
is the last hill of magnetic iron which accompanies the chain in its southward 
extension, and by reference to the Map it will he seen, that this rock, at least in 
mountain masses, is invariably peculiar to the Asiatic side of the axis, and is, 
wherever it exists, associated with porphyritic eruptions. At Yangelskaya, por- 
phyry appears in the streets of the village, and we met with no rocks of palaeozoic 
age, till we were half-way between the station of Syrtinskaya and the fortress of 
Kizilsk. 
The carboniferous limestone of greyish colour is there considerably expanded, 
and seems to fold over subjacent masses of porphyry. In it we found Productus 
Valdaicus, and two other smaller species, with Pectens, corals and Encrinites. 
This limestone is exposed on both banks of the Ural at Kizilsk, where it has a 
well-determined strike from north -north-west to south-south-east, and dips 40 to 
the west-south-west. Some of the underlying beds had a hard magnesian character, 
and a cone of porphyry protrudes on the left bank of the stream. 
A few versts to the south of Kizilsk the eruptive rocks have somewhat of a 
basaltic character, but M. Rose has shown that they are in truth augitic porphyry, 
accompanied by amygdaloid, with chalcedony and calc spar. Again, at Gruz- 
nushinsk, and thence to Berezofsk, the whole country is usurped by porphyry or 
greenstone porphyry, which occupies cliffs from sixty to eighty feet on the banks 
of the river. This is a tract of very fine herbage, and much resembles in aspect 
the richest grassy countries of the Scottish border, like which it is well-watered 
and pastoral To the south of Urtazimsk the carboniferous limestone recurs in 
1 For a detailed account of the crystalline rocks along this old line of the Cossack forts the reader 
must consult the work of MM. Hofmann and Helmersen (Geog. Untersuchung des Sud Ural Geb. 1831). 
On the west side of the line, or nearer to the Ural chain, the schists are converted into jasper, numerous 
bands of which we traversed in two other sections. See PL HI. fig. 5. and PI. IV . (V erch-Uralsk.) 
3 M 
