WU-T'AI SYSTEM, EO-PROTEROZOIC. 5 



That there is an unconformity at the base of the Shi'-tsui series, sepa- 

 rating it from the T'ai-shan complex, we do not doubt. The distinction 

 between the stratified schists and quartzites of sedimentary origin and the 

 very intricate complex of parallel bedded injection gneisses is decided when 

 they are contrasted in extensive sections. But the exact contact between 

 the two is not readily recognized. In a ravine south of the T'ai-shan-ho 

 we found a peculiar quartzite containing large crystals of red feldspar, 

 which is a recrystallized arkose, occurring at or near the base of the Shi'-tsui 

 series, on or close to the T'ai-shan gneiss, from which the material was 

 probably derived by erosion. The immediately underlying stratum is a 

 mica schist of indeterminate origin. The feldspathic quartzite grades 

 upward through quartzite containing some mica and but little feldspar, 

 into mica schists, which present great variety of mineralogical composition 

 and are in turn succeeded by quartzites which are in part magnetic. The 

 section of sediments, which has a length of eight miles, is interrupted by 

 a mass of augen-gneiss that is probably intrusive. The dip of the Shi'-tsui 

 strata in this section is from 30 to 70 to the northwest, and the repetition 

 of the quartzite on two sides of a great body of mica schists is such that 

 the probable structure is a syncline overturned toward the southwest. 



The augen-gneiss above referred to extends for three miles along the 

 T'ai-shan-ho. It has the uniformity of composition of a batholite and 

 appears to be an intrusive which has suffered shearing and metamorphism 

 with the sedimentary Wu-t'ai rocks. Northwest of it occur the strata of 

 the Si-t'ai and Nan-t'ai groups. 



Nan-t'ai and Si-t'ai are two of the five peaks of the Wu-t'ai-shan, 

 each of which is composed chiefly of the strata named after it. 



Strata of the Nan-t'ai group are siliceous marble, gray to black or 

 red quartzites, and schists, chiefly of chlorite and muscovite. They are 

 also garnetiferous and staurolitic. They occur on the southeast slope of 

 the Wu-t'ai range and are well exposed in the canyons above Shang-ho- 

 miau. The structure shows two or more closed synclines, overturned 

 toward the south, and overthrusts which eliminate the anticlines. The 

 sequence, as we interpret it, consists of siliceous and muddy sediments below 

 and calcareous deposits above. It may be continuous with or distinct 

 from the Shi'-tsui. The two groups of rocks were not seen in contact. 



The Si-t'ai group, comprising most if not all 'of the sequence seen by 

 von Richthofen, forms the mass and northern slope of the Wu-t'ai-shan. 

 It is a great body of green schists, chiefly chloritic, with beds of quartzite 

 containing magnetite, and coarse conglomerate of quartz and quartzite 

 cobbles at the base; all as he described it.* The relations with the Nan- 

 t'ai group are well exposed in the canyons on the south slope of the range. 



* China, vol. n, p. 364. 



