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| 0594 |
Report of a Mission to Yarkund in 1873 : vol.1 |
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CHAPTER VIII.
Section I.
A brief account of the geological structure of the Hill-ranges between the Indus Valley in Ladak
and Shahidula on the frontier of Yarkand territory, by Dr. F. Stoliczka, Geological
Survey of India, Naturalist attached to the Yarkand Embassy.
The following brief notes on the general geological structure of the hill-ranges alluded
to, are based upon observations made by myself on a tour from Leh viâ Changchenmo, the
high plains of Lingzi-thang, Karatagh, Aktagh to Shah-i dula, and upon corresponding
observations made by Dr. H. W. Bellew, accompanying Mr. Forsyth's camp along the Kora-
korum route to this place.
Before proceeding with my account, I will only notice that our journey from Leh (or
Ladak) was undertaken during the second half of September and in October, and that we
found the greater portion of the country north of the Changchenmo valley covered with
snow, the greatest obstacle a geologist can meet on his survey. While on our journey the
thermometer very rarely rose during the day above the freezing point, and hammer opera-
tions were not easily carried out. At night the thermometer sank as a rule to zero, or even
to 8° below zero in our tents, and to 26° below zero in the open air. Adding to this the
natural difficulties of the ground we had to pass through, it was occasionally not an easy
matter to keep the health up to the required standard of working power.
Near Leh, and for a few miles east and west of it, the Indus flows on the boundary
between crystalline rocks on the north and eocene rocks on the south. The latter consist
chiefly of grey and reddish sandstones and shales, and more or less coarse conglomerates,
containing an occasional nummulite and casts of pelecypods. These tertiary rocks extend
from eastward south of the Pangkong lake, following the Indus either along one or both
banks of the river, as far west as Kargil, where they terminate with a kind of brackish and
fresh-water deposit, containing melanie.
Nearly the entire ridge north of the Indus, separating this river from the Shayok, and
continuing in a south-easterly direction to the mouth of the Hanle river (and crossing here
the Indus, extending to my knowledge as far as Demehock), consists of syenitic gneiss, an
extremely variable rock as regards its mineralogical composition. The typical rock is a
moderately fine grained syenite, crossed by veins which are somewhat richer in hornblende,
while other portions contain a large quantity of schorl. Both about Leh and further east-
ward, extensive beds of dark, almost black, fine-grained syenite occur in the other rock. The
felspar often almost entirely disappears from this fine-grained variety, and quartz remains very
sparingly disseminated, so that gradually the rock passes into a hornblendic schist; and when
schorl replaces hornblende, the same rock changes into layers which are almost entirely
composed of needles of schorl. Again, the syenite loses in places all its hornblende, the crystals
of felspar increase in size, biotite (or sometimes chlorite) becomes more or less abundant, and
with the addition of quartz we have before us a typical gneiss (or protogine gneiss) without
being able to draw a boundary between it and typical syenite. However, the gneissic portions,
many of which appear to be regularly bedded, are decidedly subordinate to the syenitic ones.
As already mentioned, the rock often has a porphyritic structure, and the felspar becomes pink
instead of white, as, for instance, on the top of the Kardung pass and on the southern slope
of the Chang-la, where large fragments are often met without the slightest trace of hornblende.
To the north of the last mentioned pass the syenitic gneiss gradually passes into thick beds of
syenite-schist, and this again into chloritic schist, by the hornblende becoming replaced by
chlorite, while the other mineral constituents are gradually almost entirely suppressed. The
syenitic and chloritic beds alternate with quartzose schists of great thickness. This schistose
series of rocks continues from north of the Chang-la to the western end of the Pangkong lake
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