PROCEEDINGS OP THE AMERICAN ACADEMY. 



the Hwang-ho are very largely composed of fine Bediments; the propor- 

 tion of tin' irse materials in the extensive deposits of these riv< 

 Beems to be greater than it is in many of the so-called lake beds of the 

 West 



The surface of many extensive fluviatile plains Beems level as far as 

 the eye can reach. This level Burface is the bes! obtainable index of 

 the evenness of structure thai musl prevail both in the Btrata already 

 laid down beneath the plain, and in those yel to be deposited upon tin- 

 plain. In the absence of special studio ,.n the degree of continuity ol 

 river deposits, it cannot now be said how far a single stratum or a group 

 of strata, marked by recognizable peculiarities of texture or color, may 

 extend; but it may be urged that mere continuity of even bedded depos- 

 its, Buch as is reported in our western Tertiaries, even if occurring over 

 areas of many square miles, should not alone be taken as conclusive 

 evidence of lacustrine origin. Some other criterion than continuity is 

 needed to distinguish fluviatile from lacustrine deposits of fine texture. 

 No Other feature seems so likely to serve this need as the filled channels 

 and lateral unconformities that musl occur, albeit rarely, even in the finer 

 fluviatile deposits. The occasional presence of these distinguishing struc- 

 tures might readily escape notice in beds whose continuity has been 

 traced only by observations of colored strata, such as are visible at a 

 distance on the barren slopes of arid regions. 



10. The Tndo-Gangetic Fluviatile Plain. — The alluvial deposits of 

 the Indo-Gangetic plain stretch over hundreds and hundreds of miles. 

 They are well described in the .Manual of the Geology of India by 

 Medlicott and Blanford (or in the second edition by Oldham. 1893, 127— 

 458), where references are given to original articles for further details. 

 Gravels and conglomerates are abundant near the sloping borders of the 

 plain, while the prevailing material of the central area is some form of 

 clay, more or less sandy, with subordinate deposits of sand, gravel, and 

 conglomerates; but pebbles are scarce at greater distances than twenty 

 or thirty miles from the enclosing hills. Borings show the deposit t,, bo 

 hundreds of feet, and at one point more than a thousand feet in depth, 

 with no trace of marine fossils; and from this it is inferred that depres- 

 sion accompanied accumulation. Organic remains are not common, but 

 shells of river and marsh molluscs are occasionally found, and calcareous 



material is not lacking; the latter is frequently gathered in concretionary 



nodules ; it sometimes forms compact beds of earthy limestone. The (days 



bordering the Jumua, as well as the calcareous shoals of this river, have 

 yielded remains of a variety of vertebrates, including elephant, hippopota- 



