LOWER YANG-TZI. 83 



The strata below the Jurassic are Sinian, and the relation is no doubt 

 one of unconformity by erosion, but the stratification is approximately 

 parallel in the Sinian and Jurassic beds, and the contact was not seen in the 

 section described in the above quotation. In an adjoining section, however, 

 near "Hei'-ku-tsze,"* the unconformable contact of the two series was 

 observed and is represented in the diagrammatic section as one of uncon- 

 formity of dip as well as of erosion. 



CENTRAL CHINA. 



Under this head I consider the occurrence of Permo-Mesozoic strata 

 along the Yang-tzi, in the Ts'in-ling-shan, and in the Red Basin of Ssi-ch'uan. 



I begin the enumeration of the known occurrences with that which is at 

 once the most eastern and also the first recorded, the deposits in the valleys 

 adjacent to the Yang-tz'i, between Han-kow and Nan-king, as described by 

 von Richthofen, who says:f 



Sanghu sandstone and conglomerate. The deposition of the Kitau limestone ended 

 with a considerable disturbance, as the next formation follows quite unconformably. It 

 consists of a quartzose sandstone and quartzose conglomerate, interstratified with thick 

 layers of red clay, and carries a coal-bed at a place sixty miles below Hankau. Black 

 shales, which overlie the coal, carry some remains of plants. I was unable to establish 

 the thickness of this formation. 



Commencement of the outbreaks oj porphyry. The porphyritic eruptions have probably 

 continued in China during a long period while sediments were contemporaneously deposited. 

 Pumpelly was the first to direct attention to these wide-spread events. But it is only in the 

 great granitic region of the eastern coast, between Ning-po and Hong-kong, that porphyry 

 itself arrives at an extraordinary development. The Chusan islands are almost exclusively 

 composed of quartzose porphyry and its tufas, and from there southward it appears to be 

 only subordinate in quantity to the granite. I know it from my own observations on 

 island of Hong-kong, and by inference from the observations of others of the region betwi 

 that island and Ning-po. This is the most extensive development of porphyry known 

 any part of the world. 



Deposits of porphyritic tufa, sandstones, and clays. The porphyries themselves are 

 little developed on the lower Yang-tze. I noticed their first appearance in certain porphy- 

 ritic tufas which overlie somewhat unconformably the Sanghu sandstone. The latter 

 appears, indeed, from its purely siliceous character, to have been antecedent to any out- 

 break of porphyry, while the soft and impure nature of all subsequent deposits goes to show 

 that they were the tufaceous sediments of eruptions in remote regions. The visible thick- 

 ness of this formation below Hankau is about 3,500 feet. It incloses a few beds of coal 

 of subordinate value. 



Herewith ends on the Yang-tze the series of ancient formations. 



It will be observed that von Richthofen gives no clue to the age of these 

 deposits, which, in view of the unconformity at their base, probably do not 

 include the earlier transition sediments, but may comprise the Triassic and 



* China, vol. n, p. 368. 



t American Academy Arts and Sciences, vol. vni, 1869, p. 117. 



