So SMITH: GEOLOGY OF MIK1R HILLS IN ASSAM. 



a small tributary nala flows over a considerable sheet of mottled 

 brick-red and greenish trap, which can be traced for about 150 yards. 

 It rests on the gneiss, and the only rock visible above it is sandy 

 nummulitic limestone. 



The last exposure of trap that I saw, in a northerly direction, 

 was a low bank of mottled pale-blue and ochreoustrap about 20 yards 

 D elow the Nambor Falls, resting on the gneiss and immediately over- 

 laid by a series of grey clay-shales and shell limestones. JYIedlicott 

 states that " there is no trace of trap under the (supposed) creta- 

 ceous beds on the Namba." 1 The fact remains, however, that this 

 small exposure occurs ; though, as it is almost on the river level and 

 very like the grey waterworn' gneiss superficially, it might easily 

 escape observation. 



The fairly constant occurrence of the mottled earthy trap at the 

 gneiss-sedimentary junction suggests the prob- 



Summary. 



ability that the exposures belong to a continuous 

 trap-flow. I have never seen any trace of real bedding in the trap, 

 but it can only be a thin band some 30 feet in thickness, with prob- 

 ably no stratification. 



If there be a definite trap-flow between the gneiss and the num- 

 mulitics, its nearest relation should be Medlicott's ( Sylhet Trap', 

 which he considers intimately connected with the cretaceous. 



The same age would apply to the white chalk-like rock asso- 

 ciated with the trap. The former seems to resemble a rock de- 

 scribed by Mr. Theobald 2 from the Arakan, which he considered to 

 be cretaceous. The white rock of Longloi hill corresponds closely to 

 Theobald's description, but the Arakan rock is calcareous, and the 

 Mikir rock contains only a small amount of carbonate of lime. 



The coal bearing shales of Longloi, which immediately overlie 

 the white rock, must also be cretaceous, if the nala-section shows a 

 regular sequence of beds. In this case they are the only representa- 

 tive of definite, cretaceous, sedimentary rocks seen in the Mikir hills. 



1 Mem. Geol. Sur., Ind., Vol. VII, Art. 3, p. 38. 

 5 Manual Geol. Ind., p. 297. 



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