WESTWARD TO TIBET. 59 



description agrees with that of certain portions of the Sin-t'an formation 

 observed by our expedition in eastern Ss'i-ch'uan, and the position of the 

 fossiliferous limestone corresponds with that of the pink limestone in 

 which, near Ta-miau-ssi, Blackwelder found the few fossils that are doubt- 

 fully referred by Girty to the Devonian or lower Carboniferous. 



On the agreement of the observations of von Richthofen and Loczy 

 and ourselves, we may conclude that throughout northern Ss'i-ch'uan and 

 southern Shen-si the Devonian is represented by thin strata of calcareous, 

 marly, bituminous character, which nowhere attain very great thickness, 

 which may in fact be wanting in some sections, and which are conformable 

 to the Silurian (Gothlandian) below and the Carboniferous above. 



In connection with the occurrence of middle Paleozoic fossiliferous 

 strata in the western Ts'in-ling-shan it is desirable to consider the for- 

 mations of the Hei-shui series, which were observed by our expedition in 

 crossing that range in longitude 108 and which are tentatively assigned to 

 the period. They are siliceous argillites of greenish and reddish tints, which 

 more nearly resemble the Sin-t'an formation than any other that we know, 

 and appear to occur as it does, between a massive limestone below and a 

 coal-bearing limestone above. In general terms the stratigraphic similarity 

 between this sequence and that of the Paleozoic in the middle Yang-tz'i 

 region is such that we have little doubt in classing the whole as also Pale- 

 ozoic and the slate formation as middle Paleozoic. The slates include 

 quartzite and conglomerate at the base and appear to be thicker than 

 their supposed equivalents further south. We regard them, therefore, as 

 a nearer shore phase, and also recognize that they may include a more 

 complete sequence than is found in the Sin-t'an. 



MIDDLE PALEOZOIC STRATA BEYOND CHINA. 



We may next consider the distribution of Devonian strata in northern 

 and western Tibet, as determined by Obrutchov, Mushketov, Romanovski, 

 Bogdanovitch, and Stoliczka. 



The journey of Loczy, otherwise so fruitful in geologic details, gives no 

 clue to the occurrence of the Devonian in the ranges of northern Tibet. In 

 justice to him it must be said that his opportunities for observation were 

 limited by the official attitude of the Chinese authorities and the conditions 

 attending the expedition to which he was attached. Although he traveled 

 during four months within a short distance of the northern base of the 

 Nan-shan, he was able to observe the rocks in place only in two locali- 

 ties; in the vicinity of Kan-chou-fu and south of Su-chou. He describes 

 strata which he considers to be early Paleozoic, but which, as stated on a 

 previous page, are not identified by fossils and probably are of pre-Cambrian 



