CARBONIFEROUS IN GENERAL. 73 



very meager collections which have been obtained it is, however, hardly 

 worth while to attempt to distinguish the different horizons of the great 

 limestone formation in the light of present knowledge. And therefore, in 

 describing its distribution I shall refer simply to the Carboniferous, which 

 may include both lower and upper or either one of them. 



Northwestward from the Yang-tzi gorges Carboniferous limestone is 

 known to form conspicuous ranges in northeastern Ssi-ch'uan and southern 

 Shen-si,* and through the work of Obrutchovf and LoczyJ it has been traced 

 into northeastern Tibet, where it is more particularly represented in the 

 southern mountain chains of the Nan-shan. In the section observed by 

 L,6czy near Paj-suj-kiang the transition from fossiliferous Devonian strata 

 to the gray Carboniferous limestone is accurately described as one of strict 

 conformity, and this is also true of the sections given by von Richthofen 

 in the same district of northern Ss'i-ch'uan. The formation in this district 

 might readily be confused with a similar limestone of Permian age, which 

 rests unconformably on the folded Paleozoics. 



The expedition of 1903-04 found the Carboniferous limestone and argil, 

 lite constituting a recognizable terrane in the valley of the Han above Hing- 

 an-fu and in the Ts'in-ling-shan, in longitude 108 east. The characteristic 

 rocks are highly carbonaceous; they vary from limestone and quartzite 

 to black slate. Their Carboniferous age is not determined by fossils, as 

 they are more or less metamorphosed, but it is inferred with confidence on 

 the basis of their commonly carbonaceous character and their stratigraphic 

 relations.! 



The relations of the Carboniferous limestone to older rocks in northern 

 Tibet are not clearly expressed in the available literature. Such a section 

 as that of Obrutchov's of the Richthofen range|| is indefinite. The Car- 

 boniferous is represented as lying between folded masses of rocks that are 

 questionably assigned to the Silurian, it resting unconformably upon the 

 one mass and being overthrust by another. The structure itself is unusual, 

 as it is delineated, and the age of the Silurian rocks being doubtful it is 

 not possible to say what the unconformity means. If the older strata are 

 those of the Nan-shan sandstone and belong to the latest pre-Cambrian 

 (Hu-t'o) system, as has been suggested in the chapter on that subject, 

 the Carboniferous in this northern range overlaps upon pre-Paleozoic 



* China, vol. n, p. 599. 



t Central Asia and the Nan-shan Mountains, Obrutchov, vol. n, p. 356, pi. n (in Russian). Also, La 

 Face de la Terre, K. Suess, vol. in, p. 271. 



J Reise des Grafen Szchenyi, vol. I, p. 433. 



See chapter on the Han province, vol. i, p. 300. 



II Central Asia and the Nan-shan Mountains, vol. n, p. 164, fig. 130. Also La Face de la Terre, Suess, 

 vol. in, p. 232. 



