MIDDLE YANG-TZi-KIANG GORGES 605 



about N-S of aplite, pegmatite and melaphyre, which have only been 

 partly eroded in the river bed, thus leaving obstacles, which give rise 

 to rapids. 



As I already found occasion to remark in my former publication, 

 these dykes of eruptive matter in the granite and crystaUine schists, 

 I bring into genetical connection with the plication of the anticline of 

 Nan-t'ou. 



Just below Nan-t'ou finally begins the last or I-ch'ang gorge, 

 Pumpelly^ here mentions to the east of the granite area of Nan-t'ou, 

 once more metamorphic strata and says: "Those to the eastward, 

 which could not be closely examined, seemed to be gneiss trending 

 E-W and dipping about 30° to S." 



Blackwelder^ relates the following about a formation named by 

 him "the Nan-t'ou formation" which is indicated on Willis' map to 

 the north of the Yang-tzi: 



On account of the absence of fossils the age of the Nan-t'ou formation is 

 not accurately known. It lies at the base of the Cambro-Ordovician limestone 

 from which we obtained lower and middle Cambrian fossils within less than 100 

 miles, 160 km., from Nan-t'ou. Hence it is highly probable that these glacial 

 beds on the Yang-tzi are of early Cambrian age. 



Little is known at present regarding the areal distribution of the Nan-t'ou 

 glacial beds. The horizon at which they occur is exposed many miles both north 

 and south of the Yang-tzi, at the base of the escarpment which is crowned by 

 the Cambro-Ordovician limestone; but the river crosses it at one point only and 

 we had no other opportunity to see it. At the lower entrance to the Lu-kan 

 gorge Pumpelly examined the base of the limestone system, and reported 50 feet, 

 15 m., of quartzite, overlain by limestones, which contain layers and lenticular 

 masses of flint. It is probable therefore that the glacial beds do not occur in 

 that locality. 



I have not observed anything of all this, and only saw that the 

 gorges-limestone rests direct on the granite which may eventually 

 have become gneissy. "The glacial beds of early Cambrian age," 

 I am, however, at a loss to reconcile with my own observations. 



The first portion of the I-ch'ang gorge shows 10° SE-dipping 

 layers, which the river crosses almost vertically. At the same place, 

 where a diminution in the incline of the layers occur together with 

 their more slaty condition, the Yang-tzi bends round to the SSW. 



1 Smithsonian Contributions to Knowledge, Vol. XV, p. 4. 



2 Research in China, Vol. I, Part i, p. 264. . 



