112 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 
The present Indo-Gangetic plain constitutes a fluviatile deposit of 
great extent and thickness. Borings have been made at several 
localities. The deepest noted by the writer is that at Lucknow, which 
passes through 1,336 feet of alluvial deposits without showing marked 
increase or decrease of coarseness or reaching the underlying rock 
(ibid., p. 176). The prevailing formation is some form of clay, more 
or less sandy. The older deposits usually contain kankar (an impure 
concretionary limestone) while the newer generally do not. Sand, 
gravel, and conglomerates occur but are usually subordinate, except 
on the edges of the valley, the quantity of sand in the clay decreasing 
gradually as the distance from the hills increases. Pebbles are scarce 
at greater distances than twenty or thirty miles from the hills bordering 
the plain (Medlicott and Blanford, p. 396-397). The surface of the 
deposit forms a great inclined plane, with slope gradually increasing 
to as much as fifty feet in a mile next to the mountains. The high- 
est and steepest zone, ten to twelve miles wide, is formed of boulders, 
gravel, and sand of varying degrees of coarseness (Medlicott, p. 226). 
We should expect that borings near the southern margin of the plain 
would show fine sediments near the surface, while near the northern 
margin coarser sediments would overlie the finer, because the streams 
deposit the coarsest material where they emerge from the mountains 
and there the rock area encroaches upon the finer sediments. Four 
deep borings have been made in the Gangetic plain. Two that are 
favorably located for the purpose confirm the expectation admirably. 
The other two are less suitable for reference (Oldham, a, p. 475- 
476). 
The alluvial deposits of the upper Indus region have been described 
by Drew. In the fans the material is accumulated in a general way 
in layers, though of peculiar form; not horizontal, but rather in curved 
coatings. The lateral changes of position of the depositing stream 
and the partial growth of layers are denoted by false bedding (Drew, 
p. 448). Some of the fans are made up of semi-angular pieces of stone 
of material such as hardened shale and slate in masses seldom above 
the size of an octavo volume; others from granitic mountains are 
composed of more or less rounded blocks of granite which are often 
four feet in diameter; but among these there is gravel and sand of the 
same material. In some cases the material merits the. description 
“unrounded” (ibid., p. 451). If the river alluvium remains relatively 
stationary the fan gravels encroach and rest upon it. It is more usual 
for both tributary and main stream to raise their beds so that inter- 
stratification occurs at the fan-edge, a lapping for a short distance of 
