74 SMITH: GEOLOGY OF MIKIR HILLS IN ASSAM. 



great flexure 1 ; it is probably continuous along the foot of the Burrail 

 range far to the north-east, into the Naga hills. 



The massive sandstone continues northwards from Haflong, with 

 a very gentle general northerly dip and a gradually decreasing thick- 

 ness across the North Cachar hills. In the Jatinga valley and sur- 

 rounding high ranges, the shales and sandstone attain a great thick- 

 ness. The visible section must contain 5,000 feet of rock, of which 

 fully 3,000 feet belong to the massive sandstones. 



Northwards the thickness decreases greatly. Near Lumding the 

 total is certainly under 2,000 feet. It is evident that a great increase 

 in the development of the series takes place from north to south — a 

 fact which, as frequently pointed out by earlier observers, occurs all 

 along the southern margin of the Shillong plateau. 



No trace of nummulitic beds is met with across the North Cachar 

 hills, and as these are very constant throughout the Shillong and 

 Mikir hills at the base of the tertiary, it is almost certain that the 

 Jatinga shales and sandstones are of younger tertiary age — a view 

 already adopted by Medlicott. No hard and fast line can be drawn 

 between the shales and sandstone, but it is probable that they re- 

 present the lower and upper Siwaliks, though it is also probable that 

 the younger-pliocene beds are absent in the Haflong section. 



Mikir Hills. 



The Mikir hills present several difficulties to the geologist, the 

 chief of these being the great lack of rock-exposures of any kind, to 

 say nothing of any visible length of section. The country is made 

 up of low undulating hills, densely covered with jungle and tall grass, 

 the latter often 30 feet in height. The rainfall is moderate, and so 

 a very substantial coating of soil covers the whole country. On the 

 hill-tops occasional boulders give evidence of the rock below, but 

 they are seldom actually in situ. 



The hill-slopes and valleys are usually absolutely bare of any rock- 

 exposures. The larger nalas form the chief hunting-ground of the 



1 Mem. Geol. Surv., Ind., Vol. IV, Art. 3, pp. 44-48. 



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