OCT. — MAR. 1858-59.] Report of the Magnetic Survey. 355 



It is only during the middle, and towards the end of the hot sea- 

 son, that the hot winds blow till 2 or 3 o'clock in the morning, 

 when the rains stop them suddenly. 



Also, the hour of the day at which the hot winds commence, is 

 variable from the beginning to the end of the hot season. In the 

 first months they begin to blow at 12 or perhaps 1 p. m., then the 

 period becomes gradually earlier, till a short time before the rains 

 they begin at 6 or 7 a. m., leaving only a few calm hours in the 

 very early part of the morning. 



The quantity of carbonic acid during the hot winds is very 

 small. It reached in an experiment at Allygurh*, scarcely in 

 10,000 parts of air, the ordinary quantity being 3*5 to 4 parts in 

 10,000. 



Geological Observations. 

 Of the valley of Brahmapootra, 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 Hima- 

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

 this map.f 



These observations, compared with the examinations of the dif- 

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

 Brahmapootra differs from the Delta in being covered with lacus- 

 trine deposits, occasionally varied by the coarse gravel brought 

 down by the Himalayan Rivers on its North-Eastern side. 



The course of the actual Brahmapootra, 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 gradually 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, 



* The quantity of air examined was 50,000 cubic centimetres, the in- 

 crease of weight of all potassium tubes reached was not a full milleo- 

 gramme, 



t This map, in four sheets, scale four miles to an inch, has been sent 

 with my manuscripts to the Hon'ble the Court of Directors. 



