« 이전계속 »
and it appears therefore impossible to regard them otherwise than as accumulations of debris washed from the ranges into the great troughs between these ranges, and therefore posterior to the great final upheaval of the Himalayas.
Very little is known of the nature of the rocks forming the ridges, ranges and spurs in Saltoro, Nuba and Shayokh. Dr. Thomson,* on native information (Izzet Ullah), tells us that the rocks of the Shayokh and Nuha valleys are in great part primitive limestone. "The limestone continues towards Rodok and the water of the Pang Gong Tso (lake) hold a sufficient quantity of lime to form a calcareous deposit which cements the pebbles together in patches of concrete at the bottom of the lake." The water of the Pang Chong Tso is sufficiently brackish not to be fit for drink, and it has a bitterness probably due to sulphates of Soda and of Magnesia. From the examination of a specimen of the calcacerous incrustation which is formed on the shore of the lake, I found that Magnesia is about as abundant as lime.
An extremely pretty species of Limnea or rather Physa once lived in the lake, and dead shells of it are abundantly found in the baud of tufaceous deposit, a few feet above the present level of the water. These shells no longer exist in the lake (Austen). They have probably been destroyed by the diminution and concentration of the brackish water.
General Cunningham informs usf that the rocks of all the high ranges and peaks of Rodok are granite and gneiss, and this appears to be highly probable. Metamorphic rocks also abound; the mountains near the Pang Chong Tso containing a great deal of mica-schists; and crystalline marble is also found on the shore of the lake, apparently in immediate contact with granitoid rocks.
Iu the northern portion of Rodok some hot springs exist in a
locality called Chong Chin Mo; there water deposits largely a grey
tufa which is composed of carbonate of lime, sulphate of lime and
sulphate of soda. Such tufa is common near the warm springs of
the saliferian in the Punjab. Its composition is also that of the
saline impurities of the brackish lake of Tso Moreri in Rukshu, and
* "Ladak," by General Cunningham, R. E.
of the efflorescence which accompanies the borax at Pnga. From the extensive beds of gypsum and impure salt found in Rukshu, little doubt can be entertained that the saliferian is there well developed, and by analogy it is to be presumed that the same formation is also to be seen in Rodok. Borax is said to be exported from Rodok in large clean crystals, but I do not know whence they are obtained; that it does come from Rodok appears however pretty certain; and that is another resemblance with Rukshu, and another reason for believing that the saliferian is probably well developed in Rodok, and is there accompanied by hot springs and fumaroles exhaling boracic acid.
I have never seen any fossil which had been brought from Rodok, Shayokh or Nuba; it is impossible therefore to say to what age belong the beds of limestone mentioned by Dr. Thomson. The beds are called " primitive limestone;" but as Jacquemont, Vigne, Thomson and others speak sometimes of fossiliferous limestone (such as the Maims Bal limestone in Kashmir) as "primitive," it is difficult to know ior certain what is meant by that somewhat antiquated term.
79. The Korakoram Chain is a range of very great extent, beginning at the Pamer Steppes and reaching to the S. E. as far as the centre oi Thibet in longitude E. 94° and as low as latitude N. 30°. The plateau near its south-western slope is from 15,000 to 17,000 feet high, and is an arid tract of horizontal allnvian covered with loose stones and supporting very little vegetation; more to the north it is a labyrinth of wild valleys. Near the Mashabroom mountain (above 26,000 feet) the soil of the valleys between the spurs is to a great extent covered by glaciers; where not so covered, it is often an indurated clay strewed with debris of pale limestone a good deal worn and weathered, and with globular cystideae in very great abundance. Mr. Ryall, of the Great Trigonometrical Survey, gave me one of the pieces of limestone and some of the fossils. The limestone is an argillaceous dolomitic limestone, pale yellowish brown, with a few patches pale blue, weathering like frosted glass, and resembling a good deal of the rocks of the Weean and Kothair groups of carboniferous limestone. The spha-ronites, however, point to a silurian epoch, these echinoderms having not been found as yet in formations posterior to the Wenlock limestone.
The tphteronites of the Mashabroom are probably a new species; they were found in considerable variety, from the size of a small walnut to that of a large orange ; the largest were perfectly round and polished like a cricket ball, without warts, spines or facettes, pierced by numerous pores. Some of the smaller have the stems scarcely visible (fig. 6, PI. VIII), and are covered either with large tracts set well apart or with smaller ones set closer; some spines are depressed or lenticular; all are pierced by innumerable pores, none shows traces of polygonal plates; mouth not to be seen in any of the specimens I have examined. (See figs. 5, and 6, pi. VIII and plate IX fig. 1.) The discoverer, not being a geologist, did not look for other fossils: the cystideae were so numerous and so curious in appearance, that they gave quite a peculiar aspect to the ground.
The Mashabroom is stratified to its very summit, the beds being limestone and shales, dipping towards the S., at a moderate angle. This stratification is so well marked, that it can be distinctly noticed from a long way off. These sedimentary beds repose on metamorphic layers of mica-schist and gneiss. The limestone is extremely rich in magnesia, principally towards the base of the bed, where it passes into Steatite in patches (Austen). Some of the Serpentine and Jade (compact Tremolite) brought to Srinuggur and there worked into ornamental articles by the stone-cutters of that city, come, I believe, from the neighbourhood of the Mustak Range and of Mashabroom, though the greater quantity is supposed to be derived from the Yarkandkass valley and the Kuen-Luen Chain in Khotau. There can be little doubt that the limestone of the Mashabroom is the parent bed of the cystideae found in the valley between two of the spurs of that mountain ; and at least a portion of the limestone of Mashabroom is Silurian,
The following sketch-section embodies the information kindly given me by Mr. Ryall and Captain G. Austen.
<a and Afghan Mountains. 49
1, granite; 2, gneiss and micaschist; 3, sandy shales and coarso slate without fossils; 4, pale dolomitic limestone containing patches of Steatite; 5, pale ochre-coloured limestone, the probable parent rock of the SphaMonites found at the foot of the mountain.
To the north of the great glacier Baltoro is that portion of the Korakoram Range known as the Mustakh and crossed by the Mustakh Pass at an elevation of 18,400 feet. The whole S. Western face of this Mustakh is covered by enormous glaciers through which the rocky spurs of the mountains rise like islands and promontories. These rocks Captain Godwin-Austen found to be limestone dipping to the N. E., but he failed to find fossils in it, though ho noticed traces and fragments of organisms. It is so very probable that these beds are a continuation of the limestone of the Masha Brum, that I have not hesitated to colour them in the map as Silurian. Of course, this requires confirmation. Unfortunately the difficulties of reaching even the foot of these gigantic mountains aro nearly insurmountable.
80. I could not get any information on the nature of the rocks forming the remainder of the Korakoram Chain. The few European travellers who ever saw the chain, agree, I believe, in representing it as being mostly composed of granite.
On the other side of the chain we find, between it and the next parallel, viz. the Kuen-Luen Chain, the valley of the Yarkandkash (river), which extends from the Korakoram or Yarkand pass to Tashgurkhan, and the Akzai Chin or White Desert, which is continued towards the S. E., nobody knows how far. The valley of the Yarkand river and the Akzai Chin are separated one from the other by a low ridge of mountains similar to the masses of mountains found between the other great chains of the Himalaya. All we know of the valley of the Yarkandkash is that some mines of rock-salt occur there, and that both in the beds of the Yarkandkash and Karakash and in the the ravines of the neighbourhood, some pebbles are collected and used for cheap jewellery; and these pebbles are either quartzy stones or rocks decidedly volcanic. There is apparently some analogy between these mountains and those of the centre of Rupshu and of Ladak. The Akzai plain is also very similar to the countries just mentioned, in at least the one character of being an elevated, rainless desert, spotted with small lakes, some fresh, and Others salt.
It is superfluous to say that I know nothing of the Geology of the Yarkandkash and Karakash valleys and of the Aksai Chin; neither is there anything known of the formation of the Kuen Lnen or Piryukh Chain, except that it is reported to contain valuable copper and gold mines. Another small chain or range, half way between the Kuen Luen and Yarkand seems to be the last parallel of the Himalaya. Yarkand is supposed to be in latitude N. 38° and about 5000 feet above the sea. From the top of the Korakoram pass to the foot of the hills, the distance is approximately 110 miles, and the descent 13,000 feet or about 118 feet per mile, a mild slope[ for a mountainous country.
(To be continued.)