6 RESEARCH IN CHINA. 



We there find the conglomerate duplicated by overthrust, but overlying in 

 regular sequence the Nan-t'ai quartzites, and grading from conglomerate 

 through quartzite upward to schist, after the fashion of a passage from 

 basal conglomerate to fine muddy sediments. The pebbles in the conglom- 

 erate consist chiefly of quartz and quartzite, the latter being of varieties 

 that occur in the Nan-t'ai group, together with some of granite. Hence we 

 infer that the rocks below the Si-t'ai had been folded and eroded before 

 that series was deposited. The conglomerate, consisting as it does almost 

 entirely of large rounded quartz and quartzite pebbles, contains the 

 remains of a deposit that had been concentrated from a more complex 

 constitution. Before metamorphism it may have closely resembled the 

 bed of quartz cobbles found at the base of the Potomac formation of the 

 Atlantic coast, and may have resulted, as that deposit did, from a prolonged 

 cycle of erosion which ended in consequence of a marine transgression across 

 a peneplain. Moreover, in the western part of the Wu-t'ai-shan, no groups 

 corresponding to the Shi-tsui and Nan-t'ai groups were seen between the 

 T'ai-shan complex and Si-t'ai schists. This fact and the presence of the 

 granite pebbles in the conglomerate suggest an overlap of Si-t'ai strata 

 beyond the older Proterozoic rocks. 



The greater part of the Si-t'ai group consists of green schists colored 

 chiefly by chlorite. Stratification is obscured by schistosity and the struc- 

 ture can not readily be made out. It is probable that several isoclinal folds 

 occur, overtumed toward the south and separated by overthrust faults. 



On the summit of Pei'-t'ai is a small area of biotite gneiss, which may 

 be the highest stratum of the Si-t'ai group preserved in a syncline, but we 

 were not able to determine conclusively what the relations to the adjacent 

 green schists actually were. The gneiss may be an intrusive body. 



Returning to the analogy which exists between the Wu-t'ai and Huron- 

 ian systems, I may point out some of the parallel relations. The Lower 

 Wu-t'ai (Shi'-tsui group) rests unconformably upon the basal T'ai-shan 

 complex, as the lower Huronian does on the Archean (Keewatin) gneiss. 

 The Nan-t'ai group overlies the Shi-tsui and may be separated from it by 

 an unconformity, as the middle Huronian is from the lower. The two 

 series were similarly composed of siliceous, clayey, and ferruginous sedi- 

 ments, which have undergone intense metamorphism and become schists of 

 varied constitution. The upper Wu-t'ai (Si-t'ai group) is unconformable 

 to the middle Wu-t'ai as the upper Huronian is to the middle Huronian. 

 The upper group in each case consists largely of chloritic schists associated 

 with ferruginous quartzites. [Both the Wu-t'ai and the Huronian series 

 have been affected by some igneous intrusions, which occurred before the 

 strata were deformed by shearing, and also penetrated by later dikes. 

 These are but analogies, yet they serve to suggest a parallel in the ancient 



