52 MEDLICOTT^ SHILLONG PLATEAU, 



notwithstanding' its great massiveness^ and hence the presumable energy 

 of the irruptive action, it is striking how little collateral evidence 

 there is of such action. In the low ground to the west of Maophlong 

 there are numerous cases of strong dykes cutting across the strike of 

 the schists, and proving fuUy the locally intrusive character of the 

 trap. In the quartzites such instances are very rare : I have walked 

 for miles along the contact of broad masses of trap filling the ground 

 between strong ridges of quartzite without finding ever so small a case 

 of penetration by the trap ; and where these valleys of trap run into 

 each other it seems to be mostly at the folding and, elevation of the 

 quartzose strata. I only know of one instance of a trap dyke cutting 

 boldly across the quartzite ; this dyke determines a saddle in the ridge 

 at half a mile to south-south-west of Maophlong ; the strike of the 

 quartzites being steady against the sides of the trap on both sides. 

 The base of this dyke is seen under the road at the north end of the 

 cutting for the approach to the Bogapani bridge. Over the great 

 surface exposed, I have not seen any case of intrusion into the trap 

 by trap. 



Although then this rock would seem to be altogether introduced 

 into the Shillong series since the completion of that series, and by one 

 continuous process, it affects a definite position in the series : not only 

 do we find it associated with the schists, in the ground to the west ot 

 Maophlong, in a far more abundant and more intimate manner than 

 with the quartzites, but even in the region to the south-east • of 

 Maophlong it seemed to me as if the great runs of trap along the strike 

 actually occupied the position of the schists, — where these would now be 

 but for the introduction of the trap. All about Maobelarka and 

 Laisoplia the conglomerate band is in contact with the trap and presum- 

 ably rests upon it or rather in it. It seems to me necessary to suppose 

 that the trap has in many places and to a great extent absorbed and 

 assimilated the schists. 



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