STRATIGRAPHY OF CHI-LI AND SHAN-SI. 109 
WU-T’AI SYSTEM. 
Definition of the Wu-t’ai system.—Von Richthofen, in 1871, found the 
Wu-t’ai-shan and its foothills composed largely of greenish chlorite-schists, 
and certain other metamorphic rocks which were difficult to separate 
stratigraphically from each other. He concluded that they were later in 
age than the red gneiss and granite, and older than the Sinian. In his pro- 
visional table for the correlation of the general sections in various parts of 
China,* he expresses the opinion that the Wu-t’ai schists probably repre- 
sent the lower portion of the Huronian system in the United States, a corre- 
lation based, no doubt, on lithologic character. To the whole group he 
applied the name ‘‘Wu-t’ai Schichten,’’ which we retain by using the phrase 
“Wu-t’ai system.” Along the route traveled by von Richthofen, how- 
ever, only a small part of the metamorphic rocks of the Wu-t’ai district 
are visible. Coming into the region from the southeast, we crossed other 
metamorphic formations which he did not see, and, as they are related 
by their general characteristics to the Wu-t’ai schists, we have enlarged 
the term so as to include them. When the district comes to be studied 
in detail throughout, additional formations may be discovered, which do 
not appear along either of the routes thus far explored. 
The Wu-t’ai schists occur in the Wu-t’ai range for an undetermined 
distance east and west of the summit peaks, southward nearly to the 
villages of Téu-ts’un and Liu-yiian, and for several miles south of the 
T’ai-shan-ho near Shi-tsui. They were not seen in Chi-li nor elsewhere in 
Shan-si. 
The facts observed in our brief surveys of this intricate system suffice 
only to yield suggestions of stratigraphy and of structure. The sequence 
of formation and the correlation of separate sections are therefore inferred 
rather than established. The observed sections are described in the 
following paragraphs, and the inferred correlations are stated under a 
distinct head. 
DESCRIPTIONS OF OBSERVED SECTIONS. 
Shi-tsui section (Strata 1 to 20, Plate XVIII).—The rocks of the Shi-tsui 
section are exposed along the T’ai-shan-ho, from a point 14 miles, 2.5 kilo- 
meters, southeast of Shi-tsui to a point 3} miles, 5.25 kilometers, north of 
there (see Plate XVIII). In the southern portion of the section are feld- 
spathic quartzites associated with dark mica-schists and purer quartzite; in 
the middle are mica-schists and fine-grained gneisses with certain other 
rocks; and the northern end consists of magnetic quartzite and jaspillite. 

*Von Richthofen, China, vol. 1, page 378. 
