STRATIGRAPHY OF CHI-LI AND SHAN-SI. 117 
entire sequence, from the feldspathic quartzite next to the inferred uncon- 
formity, 2.5 miles, 4 kilometers, southeast of Shi-tsui, through the central 
mass of schists, to the contact of the quartzites and schists with the 
augen-gneiss 4 miles, 6.5 kilometers, above that village (Plate XVIII, beds 
2-20). The rocks are dominantly mica-schists and gneisses with thick 
layers of quartzite and thinner bodies of amphibolite. All are of sedi- 
mentary origin. 
If the strata in the Shi-tsui section succeed one upon another in mono- 
clinal succession, the apparent thickness of the group is about 12,000 feet, 
3,650 meters, subject to a correction for possible thickening in consequence 
of shearing, and for possible reduction of volume under anamorphic condi- 
tions.* But if the strata lie in a closed overturned syncline, as is suggested 
by gentler and steeper dips and by repetition of the quartzose beds, the 
Shi-tsui group consists of a lower alternation of dark schists and ferruginous 
quartzites (Nos. 2-10) and an upper mass of schistose pelites, arkoses, etc. 
(Nos. 12-18). The thickness of the former can be rather confidently 
estimated as being about 4,000 feet, 1,200 meters; while that of the mica- 
schists may be 2,500 feet, 760 meters, with a large correction for meta- 
morphic changes as suggested above. 
According to this interpretation of the structure and stratigraphy, the 
group of strata which lies next to the T’ai-shan complex, and which may 
with confidence be considered the oldest group of the Wu-t’ai system, 
consists of a normal sequence, from basal arkose, through heterogeneous 
psammites, to more uniform pelites. In spite of their immensely greater 
age, there is nothing that notably distinguishes these strata from the meta- 
morphosed psammites and pelites of the Cambrian, in the New England 
province of the United States. Thus the oldest sediments of China indi- 
cate that processes of weathering and erosion similar to those of Paleozoic 
or present time were active in an ancient Pre-Cambrian age. 
Nan-t’ar group.—In the southern part of the Wu-t’ai-shan section 
occurs a series of quartzites and siliceous marble. The quartzites are dark 
gray or reddish in alternating bands. Locally they are fissile and even 
schistose. The marble is similar in color and contains thin seams of slate 
and quartzite. The section is cut off by an overthrust, beneath which is 
a syncline in siliceous schists and white marble. 
This group of strata—principally quartzite and marble—forms the 
lower part of Nan-t’ai, the southern peak of the Wu-t’ai range, and from 
that circumstance it is named the Nan-t’ai group. 
*For discussion of this principle, see Van Hise, A treatise on Metamorphism, U.S. G.S. Monograph 
XLVUI, page 169. 
