40 God win- Austen — On the Geology of [No. 1, 



the first deep pool (where our camp was pitched), near the head of the 

 next rapid, the last of the Tertiary rocks is exposed in the water and about 

 a foot out of it, and dips south about 70°, the strata apparently- 

 falling over into a sharp uniclinal. This feature I have introduced into 

 the section from Harmatti to the Tanir Ridge as it probably extends along 

 the whole base of the hills, but is covered with the more recent alluvial 

 deposits. 



To the west of the Burroi, the sandstone range has a general dip 

 NE., but a very conspicuous longitudinal roll occurs at the second large 

 ravine west of the main gorge. The strata immediately east of this ravine 

 dip 50° W., while in the main gorge of the Burroi they have a general 

 easterly underlie, but are a good deal crushed and exhibit high dips. To 

 the west the beds are much less disturbed and again assume regular dips of 

 30° to 40° northerly, the whole series gradually ascending towards Gorusut- 

 tia to the main longitudinal axis of elevation. Looking at the hills 20 

 miles to the west of the Burroi, the dip of the lowest outer range appeared 

 20° southerly, producing a long even slope towards the plains. 



The Bisnath Plain. — I first came on this remarkable portion of the 

 country, on the road between Rangsali and Burigaon, just after crossing the 

 Borgang, which has a wide sandy bed, but a volume of water not more than 

 half that of the Burroi. The rise is sudden out of the " kadir" land of the 

 former river, and about 20 to 25 feet, succeeded at from 200 to 300 yards 

 by another of perhaps 3 feet, but very distinctly marked. The surface is 

 perfectly flat, covered with a thin growth of grass, a few of the highest 

 stalks of which may be about 6 or 7 feet high, but it is a short grass for 

 Assam. Patches of forest of a few acres in extent are dotted about here 

 and there, their limits very defined and generally round or oval in shape. 

 The plateau ends abruptly on its southern side, towards the Brahmaputra, 

 but its edge is irregular in outline, having been scooped into by the river in 

 its wanderings from side to side. Traces of the former channel occur in the 

 re-entering angles, in long crescentic pieces of water fringed with marsh 

 and high reeds and grasses ; these extend mile after mile to the main 

 river. The view from the plateau, especially off the back of an elephant, 

 is very fine, the dead level surface stretching afar, the line of horizon only 

 broken here and there by a solitary tree or by the embankment of some old 

 tank, for the day has been when all this area was thickly studded with villages. 

 The low scarps of the dry nulla east of Burigang rest-house shew that 

 there the plateau is sandy, and small rounded pebbles, mostly of quartz, 

 occur cpoite near the top of the section. On the Sudoro, however, away 

 from the influence of the ancient Borgang, reel clay predominates, as well 

 as in the scarp to the west of Partabghar, where the plain of Bisnath ends. 

 The thickness of the alluvium here appears much greater, but there is no 



