392 RESEARCH IN CHINA. 
In most respects this closely resembles the last. The specimen is 
crossed by irregular vertical cracks, filled largely with limonite. When 
large slabs are observed it becomes evident that these represent sun-cracks, 
which must have been produced while the original mud was so near sea- 
level that it was occasionally left dry. This furnishes adequate evidence 
that the conglomeratic limestones, which are found at no great distance 
both above and below this member, were formed in very shallow water. 
Mottled ferruginous limestone, No. 19.—This ferruginous gray lime- 
stone is characteristic of the upper part of the Ch’ang-hia formation in 
west central Shan-tung. 
A dense and almost aphanitic gray limestone, with many nebulous 
blotches of ocher color. Fossils are rare. ‘The thin section shows that the 
gray portions consist of finely granular calcite, while the ocherous blotches 
are composed of siderite in minute rhombic crystals partly altered to limo- 
nite. The borders of these ferruginous patches are indefinite, because 
the two carbonates mingle and shade off into each other very gradually. 
From the fact that the siderite occurs in nearly perfect crystals, while 
the calcite forms irregular grains, it is thought that the former is of later 
origin, having replaced the calcite in certain irregular areas.* 
Mottled dark limestone, No. 4.—A common phase of the upper portion 
of the Ch’ang-hia limestone. Specimen collected near Ku-shan village. 
This variety is much like the last, except that the color is varied with 
sooty gray instead of ocher, while the lighter portions have an olivaceous 
tinge. The mass consists almost entirely of finely granular calcite. Through 
this are scattered sections of the shells of trilobites, pteropods, and other 
fossils. It appears that the dark mottling is due to the irregular distribu- 
tion of carbonic matter, a large amount of which is present. 
RocxKs oF IGNEOUS ORIGIN. 
All the rocks described here are known to occur as dikes or intrusive 
sheets in strata of the Sinian system and they have not been found associ- 
ated with rocks of any other age. It is probable, however, that many of 
them are contemporaneous with the intrusions which pierce the Carbon- 
iferous and younger terranes. 
The intrusions which we observed in the Sinian rocks were porphyries 
of syenitic or dacitic character with a few basaltic varieties. The syenites 
exhibit variations which approach monzonites, granites, and diorites 
respectively. The available exposures of the dikes and sills were deeply 
weathered, and it was difficult to secure satisfactory material for study. 
On this account the identifications are not in all cases free from question. 
* See oolitic limestone, No. 11, p. 382. 
