470 RESEARCH IN CHINA. 
calcite crystals are more perfect and in many cases are separated from each 
other. The interspaces between these carbonates, as well as the entire 
central portion of the nodule, are filled with fine-grained irregularly polar- 
izing quartz, such as is characteristic of flint. In this quartzose filling 
occasional small rhombs of calcite are embedded, and the whole of it is 
colored brown by carbonic material. 
The question of the origin of the flint nodules is of interest. Structur- 
ally, these nodules are geodes. The calcite was evidently deposited from 
solution as the lining of a spherical cavity and this deposition of carbonate 
did not proceed to completion. The remaining space in the interior of 
the geode was completely filled with silica and carbonaceous matter, thus 
converting the cavities into solid bodies. In the majority of cases this 
flinty filling makes up by far the greater part of the nodule, and its supe- 
rior hardness causes it to remain prominent when the shell of calcite has 
been dissolved away. 
Black ooltte, No. 143.—A layer in thin-bedded argillaceous limestone 
of buff, brown, and black colors. This is probably the lower portion of 
the Ki-sin-ling formation of Cambro-Ordovician age. Specimen collected 
2 miles, 3 kilometers, above Ta-miau-ss’1, east Ssi-ch’iian. 
This is a dense dark-gray limestone containing countless spherical 
black bodies which average little more than 1 mm. in diameter. As the 
rock fractures these spherules are broken through at all angles. 
The circular bodies appear brown in this section because of finely 
divided carbonaceous material embedded in a mass of calcite. The spher- 
ules are rarely in contact with each other and the edges are never indented. 
Each of them is more or less completely bordered by a fringe of long cal- 
cite prisms arranged radially. The granular matrix always lies outside 
of this fringe; and in the smallest interspaces it is absent because the 
fringes fill the entire cavity between the spherules. 
The individual oolitic bodies are nearly spherical in almost all cases, 
and vary from o.5 to 2 mm. in diameter (Plate LV, Fig. C). Generally, no 
distinct nuclei can be recognized, but in one case a large rounded crystal 
of calcite plays this rdle. Usually the central portion is merely somewhat 
more coarsely crystalline, but otherwise not different from the rest of the 
granule. The outer portion of each spheroid is marked by faint concentric 
rings of brownish pigment. The body-material is calcite, but the particles 
are so minute that most of them are not visible, even under a high-power 
objective. The radial streaks seen in many oolites can scarcely be detected 
in this specimen. 
This black variety marks a stage intermediate between the red oolites 
(Nos. 14 and 10) and the black oolites (Nos. 17 and 18) of Shan-tung. 
