ROCKS FROM NORTHERN AND CENTRAL CHINA. 421 
ROCKS OF SEDIMENTARY ORIGIN. 
PSEPHITES. 
Gray flint conglomerate, No. 73.—In the hills southwest of Nan-t’ang-mei 
a heavy bed of this hard conglomerate lies unconformably upon the Ta-yang 
limestone (Algonkian). It is composed chiefly of residual flints from the 
older rock. 
The rock is a pale-brown quartzite filled with angular fragments of 
black, gray, and banded flint. It deserves the term “‘breccia,’’ but ‘‘con- 
glomerate’’ is preferred because it implies the sedimentary origin of the 
rock. 
The quartzitic matrix consists of rather coarse rounded grains of 
quartz, and rarely feldspar, cemented together by microgranular silica 
identical with flint. The flinty pebbles have been enlarged by the deposi- 
tion of such silica until their edges have been largely obliterated. The 
cement between the grains has thus become continuous with the flint 
bodies and at first glance the sand-grains seem to be inclosed in the flints 
instead of being subsequent in age (Plate LVI, Fig. C). 
This hard rock has not been perceptibly deformed since it was deposited 
and, being entirely siliceous, it has not been katamorphically altered. 
PSAMMITES. 
Dense white quartzite, No. 74.—This fine-grained pure quartzite lies con- 
formably above the conglomerate just described. Its relation to younger 
terranes is not precisely known, however, for the soft shales which seem to 
lie above it have been extensively stripped off from the quartzite ledges. 
A very pure quartzite of fine texture and gray-white color. On bedding 
planes it is stained greenish. Internally the microscope discloses small 
angular and subangular grains of quartz and subordinate feldspars. It is 
worthy of note that flint does not occur among these grains nor in the 
matrix of the conglomerate (73). The grains are embedded in an ample 
gray cement, which has the constitution of a siliceous shale, 7. ¢., a crypto- 
crystalline mass of quartz and kaolin flakes. 
Like the last, this rock bears no marks of strain nor alteration. 
WU-T’AI DISTRICT, SHAN-SI. 
In the Wu-t’ai district we include the main range of the Wu-t’ai-shan 
and the adjacent valleys of the Hu-t’o-ho and its tributaries in Shan-si 
province (see atlas sheets). The most abundant rocks of this district are 
metamorphosed Algonkian sediments belonging to two distinct systems. 
Limited outcrops of the T’ai-shan (Archean) complex and larger areas 
of Sinian strata likewise occur. Of the Algonkian systems, one is highly 
metamorphosed (Wu-t’ai system), while the other is but weakly deformed 
(Hu-t’o system) and is in many places no more altered than the Paleozoic. 
