120 PROCEEDINGS OF THE AMERICAN ACADEMY 



You may be surprised not to find in the above list of formations the 

 nummulitic limestone of Si-Tungting, which I mentioned in a former 

 letter, and which belongs properly to the system of the lower Yang-tse. 

 The reason is, that I will refrain from maintaining my former, perhaps 

 too positive assertion, before the fossils, which have so perfectly the 

 structure of nummulites, shall have been examined by an authority on 

 the subject. The structure of these shells, the occurrence, with them, 

 of certain gastropods which, though hardly determinable (on account 

 of their fragmentary condition), do not have the character of any that 

 are usually found in ancient formations, the state of preservation of the 

 fossils which permits even the color of some bivalves to be recognized, — 

 all this is in strange contradiction with the similarity of the limestone 

 of Si-Tungting to some of the most ancient limestone strata on the 

 Yang-tse. The occurrence of encrinites, too, in the former, — a fact 

 which I think I forgot to mention in my former letter, — is not in accord- 

 ance with the Eocene age of the limestone in question. I never found 

 on the lower Yang-tse any fossils resembling those of Si-Tungting. 



I am endeavoring to collect data for the geological history of eastern 

 China in recent periods. There is, among others, one very interest- 

 ing feature in the valley of the lower Yang-tse, which bears on that 

 subject. You would, in ascending the river by steamer, observe that 

 it is, in the greater part of its course below Han-kau, accompanied by 

 terraces, which rise* abruptly out of the alluvial plain to an altitude of 

 from sixty to two hundred feet above it, now approaching the river 

 closely, now remaining at a distance of several miles from its banks, 

 sometimes skirting the foot of a mountain range,' then again forming 

 an extensive table-land. You might consider them, from analogy, to 

 correspond to the so-called diluvial terraces so common in the valleys 

 of great rivers. It is a striking fact, that, on examination, the terraces 

 of the Yang-tse prove to be quite different in nature, consisting as they 

 do mostly of the upturned edges of ancient formations, not of one of them, 

 but of all, excepting granite, porphyry, and the limestones. The strata 

 are inclined at various angles, and their ends abraded in nearly hori- 

 zontal planes. On Poyang Lake, the terraces consist of the two most 

 ancient formations ( 1 and 2) ; below Han-kau, for sixty miles, they are 

 composed of the soft sandstones and clays No. 11, while near Ngan-king 

 they are built up of Tatung sediments. At Nan-king, finally, the river 

 is accompanied for about fifty miles, on either side, by terraces consist- 

 ing of the Nan-king sandstones and conglomerates, which are here in- 



