STRUCTURAL GEOLOGY OF THE WU-T’AI DISTRICT. 165 
of the Hu-t’o system, in complete unconformity. There is, therefore, no 
doubt that, after deposition of the Hu-t’o strata and before the invasion 
of the Cambrian sea, there ensued an episode of folding, which intensified 
the deformation of the Wu-t’ai schists and threw the Hu-t’o beds into open 
synclinal and anticlinal folds. 
PALEOZOIC INTERVAL. 
Movement without compression.—After the deformation of the Hu-t’o 
system in Pre-Cambrian time, there ensued an episode of erosion and 
marine planation, which resulted in a practically flat surface. In conse- 
quence of subsidence the area was covered during Cambrian and Ordovician 
time to a depth of about 3,000 feet, 900 meters, with limestone strata of 
uniform character and great extent, and possibly by other beds of moderate 
thickness, representing more or less of the Middle Paleozoic. Before the 
advent of the Upper Carboniferous, these strata were elevated apparently 
as uniformly as they had previously subsided, and the surface of the young- 
est limestone suffered more or less erosion. Upon this surface, in late 
Carboniferous time, were deposited a few hundred feet of coal-measures. 
Throughout these movements of elevation and depression, which occupied 
the whole of the Paleozoic and an interval of unknown duration in the 
Pre-Cambrian, the region was free from compressive stress of sufficient 
intensity to deform the rocks. 
MESOZOIC DEFORMATION. 
Episode of folding.—Upper Carboniferous strata are folded with the 
earlier Paleozoic rocks, in the synclines of T’ién-hua and Yau-t’6u (atlas 
sheets C I and C II), and the epoch of folding is thus placed at a later date. 
It is not possible in the absence of younger strata in this district to say 
positively how much later, especially as the evidence for other regions 
where such rocks occur is contradictory. 
In Shan-tung, the late Paleozoic strata, probably including Permian, 
appear to be folded with Jurassic beds. In the middle Yang-tzi region 
we observed apparent conformity between the folded Carboniferous and 
the K’ui-chéu (Permo-Mesozoic), of which the upper part is apparently late 
Triassic.* Thus, on the evidence of these two widely separated regions, 
between which the Wu-t’ai district occurs, we should assign the date of 
folding to a post-Triassic time. Observations in regard to the apparent 
conformity of the Jurassic or Triassic with the Permian and Carboniferous 
are not, however, conclusive; in Shan-tung the latest Carboniferous or 
post-Carboniferous strata are but slightly flexed, are associated with con- 
temporaneous volcanics, and are much faulted; their relation to the 
Jurassic is, therefore, not clear. And in Ssi-ch’uan, 200 miles, 300 kilo- 
meters, west of our route, the Permo-Mesozoic of the Red Basin lies 
*Chapter XIII, 
