108 RESEARCH IN CHINA. 
PRE-WU-T’ AI UNCONFORMITY. 
Although the relation of the T’ai-shan complex to the Wu-t’ai system 
has not been definitely observed in any locality, there is no doubt that 
the two are unconformable. The dissimilarity of the two systems is 
incompatible with any other relation; the T’ai-shan complex is appa- 
rently largely igneous and is profoundly metamorphosed like the Archean, 
while the Wu-t’ai strata are very largely of sedimentary origin and are 
rather less altered. The latter also contain arkose, probably derived from 
the T’ai-shan. 
The unconformity between the two systems may be exposed at two 
points along our route, to which we have already referred. One is south of 
Tai-chdéu, on the northern slope of the Wu-t’ai range; the other is southeast 
of Shi-tsui. 
South of Tai-chéu, Willis observed that granitoid gneiss is followed by 
quartzite and schist. For 3} miles, 6.5 kilometers, from the mountains, 
south of the plain of the Hu-t’o-ho, the gneiss forms a belt through which a 
deep canyon is cut. At its head the canyon widens to a gravel-floored 
valley with slopes of quartzite-schist and mica-schist, which appear to dip 
north about 80° toward the closely adjacent gneiss. Near the contact, for 
a width of several hundred feet, the schists are much decomposed and 
iron-stained. ‘The actual contact was not found. It is probably one of 
unconformable deposition, which is overturned; but it may also be an over- 
thrust. 
Southeast of Shi-tsui the unconformity between the Wu-t’ai system 
and the T’ai-shan complex is exposed in a continuous section, but the basal 
layers are so thoroughly schistose that the location of the actual contact 
was not determined. The lowest recognized sedimentary member is a 
coarse-grained feldspathic quartzite (stratum 3, Plate XVIII), which is 
separated from the typical T’ai-shan gneiss by soft gray mica-schists, which 
either might have been produced by extreme metamorphism of shaly sedi- 
ments beneath the quartzite, or be part of the gneissic complex. 
The mineral composition of the quartzite is such that it probably 
represents an arkose sandstone, which has since been severely deformed 
and partially recrystallized. The original feldspar fragments, which were 
worn and more or less decayed, have been extensively granulated, and 
from the product fresh feldspars have developed. The rocks of the T’ai- 
shan complex, constituting the mountains toward the east, are such as may 
have yielded arkose sediment under appropriate conditions of weathering. 
The contact thus resembles that of a basal conglomerate resting unconform- 
ably upon an older series. 
