MIDDLE YANG-TZ'i-KIANG GORGES 615 



Yang-tzi. That the effect of retrogression proved to be most power- 

 ful as near as possible to the Tsin-ling-shan appears most natural. 

 The open sides of the Nan-t'ou and Sin-t'an areas toward the north 

 quite accord with a retrogression theory for this last part of the Middle 

 Yang-tzi. 



All the grand gorges of the Middle Yang-tzi are very interesting 

 when one could see in them the fixed image of the relation between 

 the rate of movement of the earth's crust in the folding process and 

 of the cutting-power of a river. Although from Chung-king to 

 Tch'ang the Yang-tzi cuts through the anticlinal mountain ranges 

 nearly perpendicularly, there is a sufj&cient number of exceptions, for 

 instance, where the river has a meandering course in the gorges; so 

 from this point of view we cannot find either a proof to support the 

 antecedent theory, nor one against it. The indifference of the Middle 

 Yang-tzi to the general land-structure, rising from south to north, 

 might account to the antecedent theory. On the other hand the bend- 

 ing round of the Yang-tzi, near Wan-hien, from a general NNE to an 

 ENE course, in complete correspondence to the turn of the anticlines 

 of the Red Basin against the Tsin-ling-shan, seems to bear against 

 this theory, for here the river has followed the mountain structure. 

 If there has been any antecedent watercourse in this region, it must 

 anyhow have been considerably affected by the folding process, 

 probably being restored only after a retrogression process of a water- 

 course more downstream from this point. 



From the above it is clear that by reason of the present 

 condition of the investigation of the whole of the Yang-tzi basin 

 WT cannot come to a decisive opinion to attribute the origin of 

 the grand gorges of the Middle Yang-tzi-kiang either exclusively 

 to the antecedent river theory or to that of the retrogression 

 process. 



Contrary to Kniep, however, I must point out that the meanders 

 of the Yang-tzi in the synclinal valleys and even in the eastern limb 

 of the Nan-t'ou anticline were exclusively caused by the geological 

 and the rock structure. Another important example of this kind can 

 be seen in the part of the river between Wan-hien and K'ui-chou-fu, 

 where the Yang-tzi, having lowered its course to one of the thick sand- 

 stone layers of the K'ui-chou formation, here being in a horizontal 



