STRUCTURAL GEOLOGY OF THE WU-T’AI DISTRICT. 161 
which is exposed in a remarkably narrow gorge, is overridden bya body of 
red-brown earthy limestone of the Hu-t’o system, dipping gently south- 
ward. ‘The contact is one of overthrust from the south, that is, from a 
direction opposed to that of overthrusts previously observed. Further 
down the canyon of the Sing-ho, beyond an interval covered by Huang-t’u, 
we observed argillites and thin-bedded limestones of the Hu-t’o dipping 
60° to 70° south, and still further beyond we came upon the Ki-chdéu lime- 
stone. We ascended the ridge southwest of the river, and proceeding 
along it, observed the structure of the limestone in the eastern canyon 
wall. It is sketched in Fig. 50, which represents a section about 1,200 
feet, 350 meters, high and half a mile long. ‘The broad mountain surface 
is composed of a flat plate of the upper massive Ki-chéu limestone; but 
underneath are similar limestone strata, closely compressed in carinate 
folds and overturned southward; between the two is a plane of dislocation. 
The structure exhibits two bodies of strata thrust in opposite directions, 
the one under, the other over. 
The structure of the lower limestone mass corresponds with that 
of the Ki-chéu in the Shi-t’ou-ho section, and the overthrust plate is that 
which carries the coal-basins of the Tién-hua and Yau-t’6u fields. The 
thrust was observed northeast of T’ién-hua, but was not traced further 
east, though it probably extends beyond the Shi-t’ou-ho. Toward the 
southwest, between the Sing-ho and the Hu-t’o-ho, the Ki-chéu limestone 
covers a large area, and along an extension of this fault-plane is probably 
overthrust upon the Hu-t’o gray limestones; but the two series are so 
similar that we failed to distinguish the contact. 
Section on the Hu-t’o-ho.—The section on the Hu-t’o-ho south of 
Tung-yii and through the Yau-t’6u coal-fieldis simple. The Sinian system 
lies in a syncline. Along the northern margin is the unconformable, but 
undisturbed, contact with the Hu-t’o system. Along the southern, beyond 
the T’ai-shan-ho, is an anticline from which the Sinian dips 18° northwest, 
and which is high enough to bring up the Pre-Cambrian above the canyon 
bottoms, though the mountain summits for some miles further southeast 
appear to consist of massive limestone. 
In this broad and shallow syncline there are three remnants of the 
Shan-si coal-bearing series. The eastern or T’ién-hua basin is cut in two 
by the brook which crosses it. The greatest depth of the basin, corre- 
sponding to the greatest thickness of coal-measures, is about 700 feet, 210 
meters. The area of the Carboniferous strata is 2.5 miles, 4 kilometers, 
long by 1 mile, 1.6 kilometers, wide (Fig. 44). The Yau-t’du field is 
likewise a simple syncline about 6 miles, 9.5 kilometers, long and a mile 
wide. It is cut to a depth of 100 feet, 300 meters, nearly to the bottom 
of the coal-measures, and is thus completely drained (Fig. 46). The third 
