118 PROCEEDINGS OF THE AMERICAN ACADEMY 



noticed their first appearance in certain porphyritic tufas which overlie 

 somewhat unconformably the Sanghu sandstone. The latter appears, 

 indeed, from its purely silicions character, to have been antecedent to 

 any outbreak of porphyry, while the soft and impure nature of all 

 subsequent deposits goes to show that they were the tufaceous sedi- 

 ments of eruptions in remote regions. The visible thickness of this 

 formation below Han-kau is about three thousand five hundred feet. 

 It encloses a few beds of coal of subordinate value. 



' Herewith ends, on the lower Yang-tse, the series of the ancient 

 formations. The only two horizons which I consider as fairly estab- 

 lished are Nos. 6 and 8, the Devonian and the Carboniferous. To the 

 latter belongs the lowest coal-bed, and it is for this reason that I do 

 not consider the question regarding the age of the Chinese coal- 

 measures in any way as settled. It must, on the other side, however, 

 be taken into consideration, that, from a comparison of the formations 

 of the lower Yang-tse with those observed by Pumpelly near Peking, 

 the coal-bearing formation appears to be but very imperfectly repre- 

 sented in the former country. To this circumstance may have to be 

 ascribed the scarcity of workable coal-beds in the region over which 

 my observations extend. It is by no means improbable that the 

 upper beds belong to a different formation not represented in that 

 region. 



After a long interruption there were deposited on the lower Yang-tse 

 a series of apparently very recent sediments, the age of which, how- 

 ever, could in no instance be determined. 



a. Tatung deposits, a series of hard, cemented sediments of clay, 

 sand, and detritus, which, by the angular shape of the fragments and 

 their petrographical nature, bears evidence of its derivation, at every 

 place, from the next adjoining hills. These strata, though always 

 inclined in a certain direction at angles of from ten to fifteen degrees, 

 do not occupy at any place a higher level than two hundred feet above 

 the river. I did not find any fossils in them. 



b. Volcanic rocks. There is, north of Nan-king, a group of extinct 

 volcanoes, whose isolated cones rise immediately out of the alluvial 

 plain to an elevation of five hundred to seven hundred feet. Their 

 lavas are dolerite and basalt. The craters are well preserved. 



c. Horizontal beds of gravel. They are probably buried deep under- 

 neath the alluvium of the Yang-tse, as the only place where they are 

 exhibited is at the volcanoes of Nan-kin". Each of those I visited 



