246 On tlie Normal Rainfall of Bengal. [No. 3 



Assam Group. — These are all situated in the valley of Assam, on 

 the narrow alluvial plain of the Brahmaputra, the elevation of 

 which at Goalpara is about 140 feet above sea level, and at Seeb- 

 saugor, 260 miles higher,* does not much exceed 500 feet. The 

 elevated plateau to the south known as the Garrow, -Khasi, 

 Jyntiah and Naga Hills, averages from 4000 to 6000 feet, and 

 intercepts a large portion of the vapour which is brought by the 

 SW winds, direct from the Bay, and is discharged upon these 

 hills, and the plains to leeward and windward, from the first 

 setting in of these winds in March or April, up to the termina- 

 tion of the SW monsoon in the beginning of October. The 

 heaviest rainfall is at Goalpara, near the lower end of the valley 

 and at Seebsaugor, and Dibroogurh at its upper extremity, where it 

 exceeds 90 inches. In Central Assam, it appears to average 

 between 70 and 80, but it is probably higher along the foot of the 

 Himalaya, all the stations enumerated lying either on the main 

 stream or to the south of the Brahmaputra. The heaviest rainfall 

 is in June and July. 



Khasi Hills. — The station of Cherrapunji is situated near the 

 summit of the southern escarpment, at an elevation of 4100 feet, 

 and immediately overlooking the plains of Silhet. The SW 

 winds, passing unimpeded over these plains and the Gangetic 

 delta beyond, are here suddenly arrested by an almost mural 

 escarpment up which they are driven, and consequently discharge 

 their vapour in a torrent of rain, unequalled by that hitherto recor- 

 ded at any other station in the world. In a single month, [July, 

 1861,] the almost incredible amount of 366 inches is recorded in 

 the register, and the average fall of this month is not less than 

 157 inches. This enormous fall is as might be expected quite 

 local. Shillong is but 30 miles to the north and a little higher, 

 (4800 feet), but between the two stations intervene three higher 

 ridges, averaging about 6000 feet, and at Shillong, the annual 

 rainfall, as deduced from four years observations, does not exceed 

 96 inches, about the same as that of Goalparah. Records from other 

 parts of the plateau are wanting, but it is probable that Chcrra- 



* As measured in a direct line on the map. 



