ROCKS FROM NORTHERN AND CENTRAIL, CHINA. 437 
overturned and that the sandstone is really younger than the conglomerate. 
The sandstone appears to bea part of the T6u-ts’un series. This specimen 
was obtained from one of the pinkish bands in the formation (Fig. 23, a). 
A hard but slightly friable pink sandstone of fine texture. The color 
is considerably modified by opaque white and yellow materials among the 
quartz grains; these are probably decayed feldspars with more or less 
limonite. Scales of white mica are freely distributed through the rock. 
CARBONATE ROCKS. 
Red dolomite, No. 105.—This is a member of the local red shales and 
limestones which form a small but conspicuous part of the Tung-yii lime- 
stones in the ridge 4 miles, 6.5 kilometers, SW. of Wu-t’ai-hién (Fig. 23, g). 
A dense light-red limestone which fractures irregularly. The thin 
section reveals a finely crystalline mass of carbonate which is very slowly 
attacked by HCl and may therefore be regarded as dolomite. ‘The red 
color of the rock is due to the presence of hydrohematite dust, which clouds 
the carbonate. The distribution of this dust was probably effected before 
the mass crystallized, for the bands of lighter and darker color pass through 
the crystals without deviation (see No. 88, Plate LVI, Fig. D). 
SINIAN SYSTEM, 
The Sinian or Cambro-Ordovician series consists chiefly of limestone 
with shales and occasional sandstones, all of which are essentially unaltered. 
Many of the limestones are oolitic or conglomeratic, like the rocks of that 
character which have already been described from central Shan-tung. No 
igneous rocks have been found associated with this system in Shan-si. 
RocKs OF SEDIMENTARY ORIGIN. 
Hematitic sandstone, No. 108.—A local iron-bearing phase of the sandy 
basal layer of the Man-t’o red shales (Cambrian). This member lies directly 
and unconformably upon the limestones of the Hu-t’o series (Algonkian). 
Specimen from the basal Cambrian contact, 7 miles, 11 kilometers, south- 
east of Téu-ts’un, Shan-si. 
This sandstone is so completely cemented by hematite that it has the 
external aspect of pure iron ore; although the granular texture of the 
sandstone is visible, the quartz itself is not. The sand-grains are composed 
of quartz and are for the most part well rounded. They are completely 
cemented with crystalline hematite. Many of the original grains were 
peripherally enlarged with quartz prior to the deposition of the hematite; 
such enlargements tended to produce crystal shapes, and hence usually 
increased the angularity of the fragments. 
