STRUCTURAL GEOLOGY OF THE MIDDLE YANG-TZI PROVINCE. 2NGY9/ 
same or a closely related age. The sequences are essentially the same, 
although we have probably less than 1,000 feet, 300 meters, of Permo- 
Mesozoic as opposed to von Richthofen’s estimate of 2,400 feet. We do 
not include the beds 3 to 6 of B, since they appear to be later than anything 
we saw on the Ta-ning-ho or Yang-tzi. 
If the facts are as observed in northern Ssi-ch’uan and on the middle 
Yang-tzi, the episodes of sedimentation and folding have been diverse in 
the two regions as follows: 










Period. Northern Ssi-ch’uan. Middle Yang-tzi. 
Deposition of beds 4 to 6 inclusive.| Beds corresponding to 4, 5, and 6 
i No apparent unconformity of dip; not observed, but may be present; 
Later Mesozoic and : : : : : 
Bue. ta yet possible unconformity, not noted their relation to folding unknown. 
one y y by von Richthofen, but suggested by | Pronounced folding either before or 
se the coarse conglomerate (3), and by after deposition of beds 4, 5, and 
the observation of Léczy. 6 in Ssi-ch’uan. 
Deposition of the K’ui-chéu series, 
Permo-Mesozoic in- | Deposition of the beds A and lower including coal-beds. 
cluding “lower part of B (1 and 2). No folding and no obvious erosion; 
Jura” of Schenk. Pronounced folding and deep erosion. probable hiatus without distinct 
| unconformity. 
Upper Limestone deposition. Limestone deposition. 
Carboniferous. 





From this comparison we are led to infer that: (a) In northern Ssi- 
ch’uan there was an episode of folding at the close of the Carboniferous; 
whereas (6) in the middle Yang-tzi region there was none until some time, 
sooner or later, after the Triassic, and then there did occur pronounced 
deformation comparable to that which had already taken place in Ssi- 
ch’uan. Intermediately the K’ui-chdéu series was laid down and was some- 
what affected by the later folding in Ssi-ch’uan as well as in the Yang-tzi 
region.* 

*See sections by Obrutschoy across the western Ts’in-ling-shan, Mongolia, and Central Asia (in Rus- 
sian), vol. 11, Plate 1, p. 356; also in Suess, Face de la Terre, vol. 111, Fig. 35, p. 270. 
