120 RESEARCH IN CHINA. 
carbonates with some fine-grained psammites and psephites, the latter may 
be related to the former as contemporaneous off-shore deposits to near-shore 
sediments; or may succeed the former in normal sequence, from psephitic 
sediments to carbonates. 
In the one case the Nan-t’ai group would be equivalent to part of the 
Shi-tsui group. In the other case the Nan-t’ai group would overlie the 
Shi-tsui group, probably in conformable succession. We are unable to 
discriminate between these suggestions, but we regard the latter as more 
probable. There is the further possibility that the Nan-t’ai group may 
succeed the Shi-tsui unconformably. 
In regard to the relation of the Nan-t’ai strata of impure marbles and 
quartzites to the beds of purer marble and quartzite in the Shang-ho-miau 
section, our inference is governed by the apparent structure. The syncline 
in the Shang-ho-miau section is thrust under the Nan-t’ai group, and the 
strata thus appear to be younger; yet the rocks are lithologically so similar 
that no notable difference of age is suggested. We suppose that the Shang- 
ho-miau section contains an upper part of the Nan-t’ai group, and that 
within that group there is a gradation upward, from fine psammites to 
impure and to purer carbonates. 
The Si-t’ai group we regard as a distinct and younger division of the 
Wu-t’ai system, separated from the Shi-tsui and Nan-t’ai groups by an 
unconformity, and possibly overlapping on the ‘T’ai-shan complex. 
As no contact of the Si-t’ai and Shi-tsui groups was observed, our 
inference as to their relative ages is controlled by the relation of the Shi-tsui 
to the T’ai-shan complex, and by the presence in the Si-t’ai of quartzite 
pebbles which may have been derived from the Shi-tsui strata. They may 
equally well have come from the Nan-t’ai strata, and our inference is quali- 
fied by that fact, but rests on the probability that the Nan-t’ai and Shi-tsui 
divisions are parts of one conformable sequence. 
The relation of the Si-t’ai group to the Nan-t’ai is traceable in contin- 
uous section. We have drawn the line between the two at the coarse con- 
glomerate, which we regard as a basal conglomerate, and which is in 
sequence with sediments that pass from coarse to finer, apparently from the 
base upward. The quartzite pebbles in the conglomerate are such as the 
Nan-t’ai rocks would furnish. There are also granite pebbles, and in the 
finer sediments occur arkose layers, which may have been derived from the 
T’ai-shan complex. It thus appears probable that not only the Nan-t’ai 
group but also the T’ai-shan complex was eroded during Si-t’ai time, and 
thus the unconformity between Nan-t’ai and Si-t’ai becomes one of notable 
duration; for the thickness of Pre-Si-t’ai strata, including the Nan-t’ai 
and probably the Shi-tsui terranes, is many thousand feet, and warping and 
