638 ANCIENT FLUVIATILE DEPOSITS 



travellers above named, there is a striking analogy between 

 the alluvial deposits of the Valley of the Nile and those 

 occurring along the banks of the Ganges and Jumna rivers, 

 in the great alluvial valley of Hindostan. Of these the most 

 obvious is the great abundance of argillaceo-calcareous con- 

 cretions, forming an impure kind of travertine, and in the 

 lowermost beds horizontal deposits of more or less extent, 

 composed of the same kind of material. Russegger con- 

 stantly alludes to their frequent occurrence, both in the 

 conglomerates and in the indurated sand- or mud-deposits, in 

 the form of nodular concretions, varying in size from a pea 

 up to a quarter of a cubic foot, and having their centres 

 occasionally occupied by drusy cavities lined by crystals of 

 carbonate of lime. The lowermost bed, No. 5 of his section, 

 consisting of a hard dark -grey clinking limestone, appears to 

 be a modified kind of the same calcareous deposition. The 

 nodular form of these concretions is familiar to English ob- 

 servers in the ' Race,' which so thickly studs the sections of 

 the brickearth-pits in many localities in the Valley of the 

 Thames. 



§ II. Fluviatile Deposits of the Ganges. 



1. Physical Features of the Valley of the Ganges. — The vast 

 expanse of the plains of Hindostan consists of a fundamental 

 deposit of very ancient fluviatile sediment, which is developed 

 in great force, but varying in its detrital characters as we 

 follow the course of the rivers down to the sea. The valley 

 is longitudinally traversed, after their escape from the 

 Himalayan Mountains, by the Ganges and Jumna, which 

 unite at Allahabad. The segment, the Doab, constituting 

 the upper division of the plains of Hindostan, is that to which 

 the remarks which follow apply. It is comparable in some 

 respects to the tract through which the ' Blue ' and ' White ' 

 Niles flow in the lower part of their course to their junction 

 at Khartoom. The Ganges at Hurdwar, where it debouches 

 from the Sewalik hills, is, according to the results given by 

 Sir Proby Cautley, 974 feet above the level of the sea, and at 

 Allahabad 269 feet, after running a course in a straight line 

 of 472 miles, giving an average fall of nearly 18 inches per 

 mile. From Allahabad to Rajmahal in Bengal, near the top 

 of the modern delta, the average fall, according to the in- 

 structive table given by Mr. Fergusson, amounts to about 

 6 inches along a stretch of 385 miles. The Jumna river, 

 where it escapes from the Sewalik hills at Eajghat, is a 

 little more elevated ; but it runs a nearly parallel course at 

 no great distance from the Ganges, and in the inclination of 

 its bed and other physical phenomena it resembles that river 



