378 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Marcll 22, 



upwards as we ascend. The sedimentary deposits and transported 

 materials vary, as a general rule, in the same ratio. The northern 

 slope of the Sewalik Hills is overlain with a thick mass of boulder- 

 gravel, inclined at a considerable angle, and conformable to the 

 sandstone strata of which this Miocene range is composed. The 

 boulders vary from a few inches to upwards of a foot in diameter ; 

 they have undergone the utmost amount of attrition, being constantly 

 smooth and rounded into more or less of a globular form. Their 

 origin is distinctly shown, as they are invariably composed of some 

 of the rocks which form the intramontane portion of the nearest 

 river- channel, transported by violent torrential action during the 

 protracted season of flooding. Modern boulder-dejections of precisely 

 the same character, and derived from the same rocks, are seen in 

 progress of formation where the rivers debouch into the plains, con- 

 stituting rude deltas, having a flattened conoid surface, the base of 

 which is ultimately confounded with the plains. This gravel-and- 

 boulder alluviura disappears from the surface and along the beds of 

 the rivers within a short distance from the hills, and is replaced by 

 a sand or clay alluvium, which becomes the prevailing deposit down 

 to the confluence of the two rivers at Allahabad. It marks the 

 boundary of the habitat of some of the characteristic vertebrate forms 

 of the Ganges, such as the Ghavial Crocodile (GaviaUs gangetici(s) 

 and the freshwater Porpoise (Platanista Gcmgetica), which ascend to 

 within thirty or forty miles of Hurdwar, where the gravel-beds and 

 rapids of the stream terminate ; while the Crocodilus bombifrons is 

 met with in the dhoons or longitudinal valleys which lie between 

 the Himalayahs and the Sewalik Hills. 



The rivers which traverse the alluvial plain of Hindostan have 

 produced the usual eftects of powerful fluviatile action operating 

 diiring a long lapse of ages, aided by movements of upheaval or de- 

 pression, distinct evidence of which has been brought to hght by 

 deep borings in the delta. The two principal streams have gradually 

 scoured their channels down through the ancient alluvium to a depth 

 of from 100 to 150 feet below the level of the adjacent plains, thus 

 exposing a very instructive section of great extent. At the lower 

 part of this section the rivers, as in the case of the " Blue " and 

 " White " Niles, have intersected horizontal beds of argillaceous or 

 arenaceous travertine, or banks of aggregated nodular kankar, 

 which frequently foi-m dangerous subaqueous reefs or bars, ob- 

 structing boat-navigation. The Government of India undertook in 

 1828 a series of operations, which extended over seven or eight years, 

 for the removal of these and other obstacles from the bed of the 

 Jumna, in which they are most prevalent. These were conducted 

 by highly instructed oflS.cers of the Bengal Engineers, one of whom, 

 Captain Edward Smith, published an account* of the most striking- 

 facts which were observed on the occasion between Agra and Alla- 

 habad. The upper haK of the section, consisting of beds of sand 

 and clay, contained throughout, in more or less abundance, the im- 



* Journ. Asiat. Soc. Bengal, vol. iii. p. 622 (1833). 



