Geological researches in China, Mongolia, and Japan, during the years 1862-1865.

76 GEOLOGICAL RESEARCHES IN
of products of this class in place and as scattered fragments at many points on the
route across the plateau, and finally the information derived from Chinese authorities
concerning the existence within historical times of active volcanoes, among the
mountains of Manchuria to the east, and in the Tienshan of the west, all point to
a development of volcanic activity, which was formerly coextensive with the area
of the present table-land. The remains of this action still make themselves felt in
the violent earthquakes that from time to time shake the districts of northern Chihli
and the shores of Lake Baikal.
The greater flows of lavas seem to have been predetermined by the fissures of
dislocation, formed along the borders of the area that was subsequently to be elevated. Such a fissure we have seen marked by a great fault south of the Lakes
Kirnoor and Tehai.
In the present state of our knowledge of this vast region, it is, I believe, impossible to say whether, at the time of the eruption of these rocks, the present depression of the Gobi was or was not under water. That a portion of the southern edge
of the plateau was not submerged appears from the fact that where the bottom of
the lava formation was visible it was found to rest immediately on the old granitic
and metamorphic rocks. This, however, does not preclude the possibility of the
existence of undisturbed deposits under the steppe sandstones of the Gobi.
The sea in which the great steppe deposit was precipitated was studded with
islands now represented by the ridges and peaks that rise above the plains. The
surface of the plains rises everywhere toward these former islands, partly because the
deposit in its formation adapted itself partially to the original surfaces of the valleys
it fills, and partly from its thickness being increased by the tributary detritus of
the islands. The effect of such a combination of circumstances upon the form of
the surface, has been discussed in treating of the lake deposits of Northern China.
It seems not improbable that the same causes may have operated here as there, in
forming many of those lake valleys, the beds of which rest upon the steppe deposit.
The age of this extensive deposit is a question of much interest. If it is contemporaneous with the steppes and terraces of the valley system of the Orkhon and
Angara, it seems probable that the sea which left this deposit over nearly all of
what is now the plateau, was also contemporaneous, within certain limits, with that
great body of water which, extending from the polar ocean to the Caspian, occupied
all Western Siberia.
The fact, to which Baron v. Humboldt1 has called attention, that seals, identical
in species, inhabit the fresh waters of the lakes Baikal and Oron (lat. 550 N., long.
119~ E.) and the Caspian Sea, seems to refer to that period. The Oron lake is a
tributary of the Vitim, and through this of the Lena, in which no seals occur. This
circumstance points very clearly to a former water communication between these
far separated localities, and the time at which the seals of the Oron became isolated
from those of the Baikal and the Caspian falls, perhaps, in the same period with the
emergence of the great plains of Northern and Western Siberia, the deposits of
1 Hnmboldt, Kosmos, IV, p. 456. Stuttgart und Tiibingen, 1858. Pallas. Zoographia Rosso-Asiatica, 1818, p. 115.