Physical geography. By Mary Somerville ...

68 PHYSICAL GEOGRAPHY. CHAP. IV.
extencs even to our dominions in Hindostan, where the formations
containing gold are unexplored.'
The sedimentary deposits in this extensive mountain-range are
more ancient than the granite, syenite, and porphyries; consequently
these igneous rocks have not here formed part of the original crust
of the globe. Rocks of the Palmeozoic series occupy the greater
part of the Altai, and probably there are none more modern. There
are no volcanic rocks properly speaking, ancient or modern, west of
the Yenissei, but they abound to the east of that river, even to
Kamtchatka, which is full of them.
The physical characters and the fossil remains of this extensive
mountaii system have little relation with the geological formations
of Europe and America. Eastern Siberia seems even to form an insulated district by itself, and that part between the town of Yakoutzk
and the mouth of the Lena appears to have been raised at a later
period than the part of Siberia stretching westward to the Sayansk
mountains; moreover, the elevation of the western part of the Altai
was probably contemporaneous with that of the Ural mountains.2
On the whole, the chains in the direction of parallels of latitude in
the Old Continent are much more numerous and extensive than
those in the direction of the meridian; and as they lie chiefly
towards the equator, the internal forces that raised them were probably modified by the rotation of the earth.
The table-land of Tibet is only 4000 feet above the sea towards
the north, but it rises in Little Tibet to between 11,000 and 12,000
feet. The Kuen-lun, the most southerly of the two diagonal mountain-chains that cross the table-land, begins at the Hindoo Coosh, in
latitude 350 30', being, in fact, a branch of that chain, and extends
eastward in two branches, which surround the lake Tengri-Nor, and
again unite in the K'han of eastern Tibet. The most southerly of
the two branches known as the Ice Mountains, and which is crossed
by the Kara-Koruml Pass, 18,600 feet above the sea, maintains a
curved course parallel to the Himalaya, and then bends north towards
the Kuen-lun, which pursues a more direct line across the table-land.
Chains more or less connected with these form an elevated mountain
plain round Lake Koko-Nor, nearly in the centre of the table-land,
from whence those immense mountain-ranges diverge which render
the south-western provinces of China the most elevated region on
earth. The country of Tibet lying between the Himalaya and the
t Sir Roderick I. Murchison.
- From the observations of Sir Roderick Murchison, M. Middendorf, IM.
de Verneuil, and Count Keyserling, it appears also that the low land of
Siberia has been extended since the existing species of shell-fish inhabited
the northern seas; a circumstance that may have rendered the Siberian
climate still more severe, and materially affected that of all the northern
parts of Europe and Asia.