266 RESEARCH IN CHINA. 
is a massive gneissoid gray granite,* of which the minerals are quartz, 
plagioclase, biotite, and hornblende, with some epidote, magnetite, etc. 
The quartz and the feldspar are white or colorless, and, being associated 
with blackish hornblende and biotite, give a notably speckled, black-and- 
white aspect. In texture the rock is moderately coarse and evenly grained, 
the dark minerals appearing usually as larger crystals. 
This granite lies beneath Cambro-Ordovician sediments in obvious 
unconformity. As it was not found associated with other Pre-Cambrian 
rocks, it is not possible to correlate it with any of the systems of that era 
which were seen in northern China; but as it is not notably schistose or 
gneissoid, we regard it as an intrusive of Algonkian, and possibly late 
Algonkian, age. 
Other Pre-Cambrian rocks, which we did not see in place, occur as 
boulders in the Nan-t’ou Cambrian formation overlying the granite. They 
consist of hornblende-schists, mica-schists, dioritic and other igneous 
rocks, and calcareous ferruginous clay slate. Pumpelly also mentions the 
occurrence of ‘“‘hornblendic and chloritic schists’’ with highly inclined 
schistosity, bordering the granite near the entrance of the Lu-kan gorge.f 
From this it is inferred that the granite is merely a late intrusive in a 
metamorphic complex, which is possibly equivalent in stratigraphic posi- 
tion to the T’ai-shan complex of north China. 
Pumpelly states that along the western edge of the granitic area the 
rock is apparently a syenite, containing plagioclase, brown mica, horn- 
blende, magnetite, and a little quartz. Evidently the rock he describes 
is merely a phase of the Huang-ling granite which is poor in quartz. 
UNCONFORMITY AT THE BASE OF THE PALEOZOIC. 
The contact of the granite with the overlying sediments was not actu- 
ally seen, but the character of the basal Cambrian rocks within a few 
feet of that contact leaves no doubt as to the nature of the division. They 
are coarse brown sandstones containing conglomerate which increases in 
prominence as the base is approached. The pebbles in the conglomerate 
consist almost entirely of small fragments of the gray Huang-ling granite. 
It is hardly necessary to add that the sandstone exhibits no effects of 
contact metamorphism, as it would if the granite had been intruded into it. 
The time represented by the gap in the stratigraphic sequence is at 
least that required to erode off the rocks which overlay the granite at 
the time when it was intruded, and may include several epochs of erosion 
and deposition, up to the end of the Algonkian. 

*In the strict sense this is quartz-diorite, but the word granite is used here in its older and more 
comprehensive meaning, viz, a rock composed of quartz, feldspar, and accessory minerals, 
{ Smithsonian Contributions to Knowledge, vol. xv, page 4. 
