568 Beport on the Magnetic Survey, [No. 6, 



in 10,000 parts of air, the ordinary quantity being 3.5 to 4 parts in 

 10,000. 



Geological Observations. 

 Of the valley of the Brahmaputra, a detailed map has been pre- 

 pared, showing the different soils, with observations on former 

 levels and beds of the river, and depths from the surface deposits 

 to the sub-soil. Different coal localities in the Bhootan Himalayas, 

 and in the Naga Hills, have been examined and entered in this 



map * 



These observations, compared with the examinations of the dif- 

 ferent soils of the Delta of the Granges, show that the valley of the 

 Brahmaputra differs from the Delta in being covered with lacustrine 

 deposits, occasionally varied by the coarse gravel brought down by 

 the Himalayan Eivers on its North-Eastern side. 



The course of the actual Brahmaputra, originally flowing in the 

 bed of the Lohit, (which was the original name used in this valley,) 

 has not been altered by a sudden change of its bed, but has gradu- 

 ally shifted itself ; the deposits made on the right bank (where all 

 lacustrine soil is carried away and replaced by the actual deposits 

 of the river) being very different from the clays on the left. 



In the Himalayas, along the North-East side of the Brahmaputra, 

 the coal is found in small seams of sand-stone alternating with 

 strata of conglomerates of pebbles (Nageflue,) the pebbles being re- 

 markably smaller than the deposits of the present rivers. 



To these sedimentary rocks succeed, at a short distance from the 

 banks (much shorter than in the Western Himalayas,) crystalline 

 hornblendic rocks, chiefly hornblendic gneiss, with a peculiar linear 

 arrangement of quartz nodules succeeding each other, when seen, in 

 the proper section, like beads on a string. 



The dip of the stratification in the sand-stones and conglomerates, 

 which form the outer ranges of the Bhootan Himalayas, is very 

 well defined by the alternation of the finely grained sand-stones 

 with the conglomerates. 



The dip of the strata is North 30 degrees to 40 degrees West, 

 inclination 55 degrees to 05 degrees. 



* This map, in four sheets, scale four miles to an inch, has been sent will my 

 manuscripts to the Hon'ble the Court of Directors. 



