ROCKS FROM NORTHERN AND CENTRAL CHINA. 379 
The red bodies range in diameter from 0.5 to 3 mm. In shape they 
tend toward sphericity, but they are often ellipsoidal or even irregularly 
rounded. They are never angular. A typical corpuscle may be described 
as being composed of a distinct nuclear body of crystalline calcite, sur- 
rounded by a succession of very thin concentric layers made up of particles 
too small to be seen even under a high power. The color of the individual 
rings varies from light to dark reddish-brown and thus gives the section 
a banded appearance. The majority of the bodies are also traversed 
by long irregular blotches of dark-red material which radiate out from 
the nucleus. Such structures are characteristic of the oolites described 
by Teall,* Wethered,t Harker,t and others. 
This typical description does not apply equally well to all the corpuscles. 
In some the nucleus is not distinct. Some are broken and recemented; 
while others are cavernous, the cavities being filled with clear calcite. 
The ratio of prominence of the radial to the concentric structures is variable 
and in different cases either may eclipse the other. 
This specimen also shows in many places masses of little tubules 
similar to those which have been named Girvanella. Wethered§ believed 
that tubes of this character which he found in British oolites were the 
remains of algee and that in many cases at least the building of the entire 
oolitic body should be ascribed to them. In this case, however, the facts 
tend to show that the Girvanella tubes were developed independently 
of the formation of the corpuscles, being sometimes older and at others 
subsequent. They occur principally in the cement between the spheroids 
or in the cavities in the latter. In the second situation the concentric 
bands in the nodule bend out around the mass of Girvanella, as if the alga 
had grown im situ, thus bulging the cavity and causing a distortion of the 
surrounding mass. 
The main points of interest in this slide are: (a) The distinct nuclei; 
(b) The clearness of the concentric and radiate structures, and (c) evidence 
that Girvanella is not the cause of the oolitic structure but is an independent 
growth. 
Red oolite, No. 10.—A thin local limestone in the lower part of the 
Man-t’o red shale formation in the hills about Ch’ang-hia. The specimen 
is closely similar to the last described, but presents some additional features 
of interest which should be mentioned. 
In color this rock is more uniformly red than No. 14, because the iron 
oxides are freely disseminated in the matrix as well as in the oolitic bodies. 
There are also other impurities, such as bodies of quartz, glauconite, and 
* Teall: Mem. Geol. Surv. Jurassic Rocks of Britain, m1, Iv, v. 
+ Wethered: Quar. Jour. of the Geol. Soc., London, May, 1895. 
{ Harker: Petrology for Students, p. 255, Cambridge University Press. 
§ Loe. cit. 
