362 PROCEEDINGS OF THE AMERICAN ACADEMY. 



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

 tion of line to coarse materials in the extensive deposits of these rivers 

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

 West. 



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

 the eye can reach. This level surface is the best obtainable index of 

 the evenness of structure that must prevail both in the strata already 

 laid down beneath the plain, and in those yet to be deposited upon the 

 plain. In the absence of special studies on the degree of continuity of 

 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, such 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 must occur, albeit rarely, even in the finer 

 fiuviatile 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 Indo-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, 427- 

 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 to be 

 hundreds of feet, and at one |)oint 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 clays 

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

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



