THE WESTERN KUEN-LUNG. 63 



the series of gray schists, quartzites, and limestones, is considered older 

 than that of gray, green, and lilac shales, which we take for Devonian." 



These older schists, quartzites, and limestones belong to that series 

 which has been considered early Paleozoic, but which I correlate tentatively 

 with the late Proterozoic. I shall refer to it again in connection with Pale- 

 ozoic diastrophism. 



Having referred briefly to the structure of the fourth chain, which is 

 but imperfectly known, but which is undoubtedly formed by beds of 

 Paleozoic strata, in part at least, Suess proceeds:* 



The structure of these four ranges of the Nan-shan, from the oasis of Kan-su to the 

 vicinity of the valley of Bouk-hai'n-gol thus presents the following characteristics: gneiss 

 is seen only upon the southern flank of the To-lai'-shan; all the rest of the mountainous 

 region is formed of closely folded Paleozoic sediments. Near the northern margin there 

 are suggestions of an overturn toward the north ; in the interior of the mountains the beds 

 appear in a vertical position or exhibit a movement toward the south. The gneissic zone 

 is not associated with the lowest strata of the Paleozoic series, as would be expected in the 

 normal succession, but instead with the Upper Carboniferous. 



The observations of Obrutchov in the southeastern portion of the Nan- 

 shan, as quoted by Suess, show that the pre-Carboniferous Paleozoic strata 

 are present in that part of the range. There can be no question but that 

 outcrops of Devonian strata extend from the vicinity of Lan-chou south- 

 eastward along the trend of the mountain chains to southwestern Shen-si, 

 in the region where Loczy collected fossils of that period near Paj-suj-kiang. 



Proceeding westward from the Nan-shan range, along the southern 

 margin of the Gobi, we have in the western Kuen-lung a section by Bog- 

 danovitch across the ranges adjacent to what is known as the Valley of the 

 Winds. I again quote Suess :f 



One of the sections which Bogdanovitch observed across the western Kuen-lung 

 crosses the Valley of the Winds. Coming from the north the first chain, the Altyn-tagh, 

 is formed of Devonian with masses of granite, exactly as in the Russian range which lies 

 far to the southwest. The second chain, the Youssoup-alyk-tagh, which follows the Tchi- 

 men-tagh, is a broad band of gneiss. The Valley of the Winds corresponds to a Carbon- 

 iferous syncline. This section, which somewhat further west is extended southward, first 

 comes to the opposite limb of the syncline, then to the steeply inclined Devonian and the 

 great granite massif of the Kyzyl-oungouin-in-tioure, beyond which there succeed further 

 outcrops of Devonian strata. It is in the region beyond this massif that there rises the 

 Ailik-tagh, where Bogdanovitch found at a great altitude "polypiers" of middle Devonian 

 age.J 



*La Face de la Terre, vol. in, page 237. 

 ]lbid., page 243. 



JSee also Beitrage zur Stratigraphie Zentral Asiens, Suess in Denkschriften der k. Acad. der Wiss., 

 Wien, LXI, 1894, p. 435. 



