STREAMS FLOWING ACROSS THE FLANKS OF THE CHAIN. 
345 
boldt, occurs in an upland valley north-east of Zlataust, which sends one rivulet 
to feed the Miass upon the east and another to the river Ai upon the west ; but 
these are mere exceptional streamlets, and are not navigable by the smallest boat 
or canoe. 
Nor can the Ural or Yaik itself be said to cut through the chain, for it flows 
southwards along the eastern flank of the mountains, so long as they maintain 
their lofty character. It is only when they apparently terminate, by subsiding for 
a considerable space into the low tracts of the Kirghis, that this river finds an 
issue to the west in a wide transversal valley, and passing in which from Orsk by 
Orenburg to the Caspian, it is prevented from flowing southwards to the Aral, by 
the high grounds which in the broad sense before stated form the southern pro- 
longation of the Ural Mountains. 
We conceive, indeed, that nearly all transverse gorges by which rivers escape 
across ridges from one water basin to another, are nothing more than ancient 
apertures in the crust of the earth which have resulted from former oscillations 
and consequent disruption and denudation of the rocks. For although cases are 
known in which the strata on either side of a gorge do not exhibit signs of un- 
conformability or dislocation (and such may be cited as examples of pure denu- 
dation only), still we believe that even in such exceptions, the transverse chasm has 
been mainly produced by a great vibratory movement, giving rise to a fissure, the 
depth and size of which has been augmented by powerful denudation when the 
land and waters were changing their relations. We maintain that highly inclined 
or torrential streams only can have made a perceptible impression in laying open 
mountain gorges which were not natural fissures ; or, in other words, that rivers, 
properly so called, have never cut sections through chains, but simply flow m chasms 
prepared for them. Remarkable examples of such phenomena are to be seen on 
the flanks of every great mountain chain from the Alps to the Andes, and on a 
smaller scale in numerous parts of the British Isles'. 
But if the crest of the Ural chain be not rent by distinct transverse gorges, its 
flanks and counter-forts, both on the east and west, expose many such in which 
flow streams, some of them navigable. We therefore took advantage o the ere- 
brianka and the Tchussovaya on the west of the ridge, and ot the Issetz and Sosva 
on the east ; and as these rivers flow respectively from east to west and west to 
. See Silurian System, pp. 206, 122 etpa.s-, ««->** •* ^ 
tin, on the Weaken, &c, in the Transactions and Proceeding, ot the Geological Society of London. 
