SILHET TRAP, 33 



species in the Theria beds which appear to be peculiar to the locahty, 

 and most of which are new." 



The exact horizon of this Theria bed is not easily determinable; the 

 ground being much covered and the strata disturbed -, I should say it is 

 decidedly nearer to the base of the series than the Laisophlang bed, a 

 conjecture that is apparently opposed to the fossil evidence^ the Ootatoor 

 group being lower than the Arrialoor group in Southern India. It is 

 certain, however, that the Theria locality was farther from the cretaceous 

 coast line than the present outcrop at Laisophlang ; and it may be subject 

 for consideration how far the very decided difference in fossil contents 

 may be attributed to this circumstance. 



6. The Silhet Trap. 



After noticing separately the .several groups of the newer sedimen- 

 tary rocks— which; however great their entire range in geological time, 

 exhibit such very marked stratigraphical affinities and regularity of 

 sequence, and which are here separated from the next older sedimentary 

 rocks (those of the Shillong series) by such a vast hiatus in the geolo- 

 gical record; — it would be appropriate to attempt some general sketch of 

 the history of this region as indicated in the mode of formation and 

 in the preserit condition of those deposits. But there is another 

 great formation to be described, which though distinguished most 

 completely from the overlying cretaceous deposits, seems to have some 

 structural connection with this later history, and to be completely cut 

 off from the next preceding period of which any positive record remains. 

 This nearly isolated formation is the stratified trap so extensively exposed 

 along the south base of the Khasia hills. 



In my former paper* I showed that all the igneous rocks of the 

 Khasia hills were of precretaeeous age. I further called marked atten- 

 tion to the great Kthological difference between the dense amorphous 

 greenstone of the interior and the stratified trap at the south base of 

 * Mem. Geol. Surv., India, Vol. IV, page 418. 



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