OBRUTCHOV, NAN-SHAN RANGE. 21 



geological relations. As constituent rocks of the Archean he repeatedly 

 mentions gneiss, mica schists, amphibole schists, crystalline limestone, 

 mica phyllite, gneiss-granite, and biotite-muscovite granite. 



Referring apparently to the same series of ancient crystalline rocks, 

 Obrutchov frequently employs the terms "metamorphic sandstones and 

 schists." With reference to the Barun Ula range,* he says: 



The axial part of the range is chiefly composed of red and green Archean gneisses 

 dipping steeply inward on both slopes, that is, forming a remnant of an ancient syncline. 



In various sections of the different constituent ranges of the Nan- 

 shan system which he crossed, for example in that of the Potanin range, f 

 he distinguishes a group composed of gneisses, quartzites, micaceous 

 schists, and intrusive granite, from semicrystalline schists, quartzites, and 

 limestones. Describing a section across the Richthofen range, he says : 



On the southern slope we see a thick series of supra-Carboniferous deposits, forming 

 one of the southern ridges, the divide of the range. They strike north-northwest diago- 

 nally across the range and dip steeply inward on both sides. Below the peak Yang-kou-er 

 appear more ancient formations, namely gray sandstones and shales, slightly metamor- 

 phosed, which I consider early Paleozoic. They do not closely resemble the ordinary 

 metamorphic sandstone and schists of the Nan-shan and other parts of central Asia where 

 I have seen them. Perhaps they are Silurian, perhaps still older. 



It is much to be regretted that Obrutchov 's third volume, in which 

 he proposed to interpret the notes published in the two now available, 

 has not appeared. As they stand the voluminous accounts of his observa- 

 tions offer little more than detached petrographic descriptions, from which 

 geologic relations can hardly be deduced. 



L,6czy distinguishes a system which he describes under the name 

 Nan-shan sandstone, and which, after having studied von Richthofen's 

 second volume, he referred provisionally to the Wu-t'ai and Sinian systems, 

 but he did so only with the reservation that the correlation is suggested, 

 but not established, by the likeness in lithologic character and degree of 

 metamorphism exhibited by the rocks of the several systems. Regarding 

 the Nan-shan sandstone, he states that it consists chiefly of gray-green 

 sandstones and clay slates, which are frequently traversed by distinct 

 cleavage or schistosity and which are barren of fossils, except for occasional 

 indistinct impressions, that may possibly be ascribed to fucoids. From 

 the various sections and descriptions given in his chapter on the northern 

 slope of the Nan-shan range, t it appears that the Nan-shan sandstone is 

 very intimately folded and is intruded by large masses of granite. 



* Central Asia, North China, and the Nan-shan. Obrutchov, vol. n, p. 79 (in Russian). 



\Ibid., vol. II, p. 115. 



t Reise des Grafen Szechenyi, vol. I, pp. 532-559. 



