ROCKS FROM NORTHERN AND CENTRAL CHINA. 381 
the iron oxide was introduced during the process of building the oolitic 
bodies. Since the original deposition, a portion of hematite appears to have 
been rearranged. One result of this rearrangement was the production of 
the radial streaks; for whether these represent fissures filled with iron 
oxide or a replacement of previously existing material along these streaks, 
they are obviously of somewhat later age than the concentric banding 
which they interrupt. Here and there a corpuscle has developed a 
granular texture by crystallization of the calcite. In these cases the hema- 
tite has been redistributed in the form of a network, inclosing the visible 
grains of carbonate, to the destruction of both radial and concentric 
markings (Plate LV, Fig. B). 
Black oolite, Nos. 17-18.—These specimens came from the black oolitic 
portion of the Ch’ang-hia limestone near the village of that name. They 
represent the typical phase of the Sinian oolites (or globulites) of east China. 
In this variety an abundance of little black nodules are embedded in 
a dense matrix, the color of which is brownish-gray. The black nodules are 
seen to be coarsely crystalline and composed of a carbonate, the black 
color of which is probably due to the presence of carbonaceous impurities. 
The two specimens are alike, except that in the first there are many large 
corpuscles (2 to 4mm. in diameter), while in the second the majority are no 
larger than mustard seed. 
Under the microscope (Plate LV, Fig. D) the little nodules appear as 
light-brown bodies set in a clear matrix. They range from 0.25 to 4mm. 
in diameter and are rounded in form, with a tendency toward spherical 
shape. The largest bodies are usually composed of several smaller cor- 
puscles cemented together and all inclosed in a single crust. In addition 
to these spherules one of the slides contains several tapering sections which 
appear to be the shells of a pteropod (/Hyolithes cybele Walcott), which is 
known to occur in large numbers in this formation. One of these shells 
contains three of the small oolitic bodies. 
Both matrix and spherules of these specimens consist of a medium- 
grained mosaic of calcite. As a rule the spherules consist of elongate and 
irregular crystals of calcite, which are often arranged in rudely concentric 
layers or in spiral whorls surrounding the center. In the other cases the 
calcite is of coarser grain and possesses no definite orientation; this decrease 
in the number of calcite crystals occasionally reaches a limit where the cor- 
puscle contains only a single large crystal of carbonate. Here and there in 
the crystal one sees little cloudy rhombs of dolomite and other crystals of 
the same shape which possess numerous inclusions of iron oxides and are 
therefore to be regarded as siderite. 
