STRATIGRAPHY OF SHAN-TUNG. 21 
intrusions the older rocks are usually intersected by numerous veins of 
quartz and red or white pegmatite, which were in some cases traced into 
actual connection with dikes of granite. Some of the quartz veins, how- 
ever, fill fissures and fault-planes in the granite itself, and must therefore be 
considered younger than the pegmatites and veins just mentioned (Fig. 3). 
LATER INTRUSIVES. 
There are associated with the T’ai-shan complex certain igneous rocks, 
which are but little deformed and are younger than any of the mem- 
bers previously mentioned. Some of them are certainly Pre-Cambrian 
in age, while others are Post-Carboniferous; in the majority of cases, how- 
ever, it is not possible to determine whether a given dike belongs to the 
T’ai-shan complex or is to be referred to a later system. In the east 
base of Man-t’o butte, in the Ch’ang-hia district, a greenstone dike, which 
traverses the red granite, is cut off at the unconformity beneath the Cam- 
brian shales. The altered basalt dikes on the T’ai-shan are believed to 
be Post-Cambrian because they resemble certain dikes in Sinian strata 
farther to the east.* 
UNCONFORMITY AT THE BASE OF THE SINIAN. 
In the districts which we visited in Shan-tung, there is always a marked 
unconformity at the base of the Sinian system. The hills on the west side 
of the valley at Ch’ang-hia afford excellent opportunities to study this 
contact. Other exposures, equally as good, are to be found between 
Sin-t’ai and Yen-chuang, and elsewhere wherever the Sinian system and 
the basal complex are found in undisturbed relations. The basal sediments 
lie upon a relatively flat surface, which has been sculptured from the T’ai- 
shan complex—a plain so well developed that the hard granites and soft 
schists had been reduced approximately to common base-level. The 
absence of coarse, clastic sediments at the base of the Cambrian indicates 
that, as the sea finally invaded this ancient peneplain, it encountered few, 
if any, prominent inequalities and that opportunities for coastal erosion 
were at a minimum. 
The time represented by this unconformity is a period long enough 
to admit at least the uplift of the region and a subsequent epoch of erosion 
sufficient to uncover the granites and to reduce both hard and soft rocks 
to a plain. The break may also represent a much greater lapse of time, 
corresponding to epochs of erosion and deposition, of which the record 

* Detailed and systematic descriptions of the different varieties of metamorphic and igneous rocks 
found in the T’ai-shan complex are given in the special report on Petrography, Chapter XVI. 
