STRATIGRAPHY OF SHAN-TUNG. Zia 
the exterior of each spherule there is a fringe composed of needle-like 
crystals of calcite, all arranged with their axes perpendicular to the periphery. 
There is still a third phase of the oolite, which is quite different from 
either of those described, and is represented by a specimen from the thin- 
bedded limestones at the base of the Ch’ang-hia formation. In this case 
the spheroidal bodies are coarsely crystalline, as may be seen in a glance 
at the hand specimen. Frequently individual spheroids consist of one 
crystal only, or there may be several rather large interlocking crystals in 
a group.* 
The red oolite, the second one mentioned, has the usual character of 
oolites described from other countries. The first and third varieties, par- 
ticularly the latter, are not so familiar. I am of the opinion, however, 
that they all belong to one category, namely, that they are true oolites 
in different stages of alteration. The several varieties of rocks of this 
character which we collected in China appear to form a graded series. 
The red variety just described is a typical unaltered oolite, in which the 
spherules are composed of distinct nuclei, surrounded by concentric layers 
of very finely divided calcite. The second step in the series is represented 
by rocks from the Sinian of the Yang-tzi gorges; in these there is a central 
nucleus which is distinctly crystalline, surrounded by faintly concentric 
layers, in which crystals are visible, though minute. The dark variety, 
first described as characteristic of the Ch’ang-hia limestone, represents a 
third stage; both nuclei and concentric banding are almost obsolete, and 
the entire spherule is composed of distinct interlocking crystals. Another 
specimen from the Yang-tzi valley shows even coarser crystals in the oolitic 
bodies. The last of this series is the third variety described above; here 
the calcite is so coarsely crystalline that individual spherules are not 
infrequently composed of a single crystal. In this last variety only a very 
few of the bodies show any traces of banding. On the basis of this series 
I advance the hypothesis that all of these rocks are oolites in different 
stages of crystallization; that the latter members of the series have been 
derived, by the crystallization of the minerals, from rocks similar, except 
in coloration, to the first variety. As the minute crystals of the true oolites 
are enlarged, the identity of the nucleus and of the concentric layers is 
gradually lost—the process apparently beginning at the center of the 
nodule and extending outward until the periphery is reached. When the 
entire mass has become distinctly crystalline we have a rock like the third 
specimen in the series. The logical continuation of the process results 
in the production of the coarsely crystalline fourth and fifth varieties. 
The possibility of this transformation depends upon the well-known fact 
* For detailed descriptions of oolites from China see special report on Petrography, Chapter XVI of 
this volume. 
