8 OLDHAM : GEOLOGY OP MANIPUfc AND NAGA HILLS. 



strike and a high, generally vertical dip are seen. The ridge to the 

 west of the Tiki valley, which culminates in the peak of Koupru, is 

 capped by sandstones dipping to the west at about 40° ; I was unfortu- 

 nately unable to cross this ridge and examine the rocks, and therefore cannot 

 of my own observation declare that these do not belong to the same series 

 as the slates below, but have good grounds for separating them, and shall 

 recur to this subject further on. In the Angami Naga country quartz- 

 ites are found not unabundantly interbedded with jet black and grey 

 slates ; the strike of these is subject to occasional variations, but the 

 irregularity of strike mentioned by Major Godwin- Austen is mostly su- 

 perficial and due to the action of gravity on rocks whose joint planes 

 have been loosened by weathering, for wherever the rock is exposed in a 

 deep gully or valley, the strike is almost invariably north and south and 

 the dip generally vertical. These rocks I refer without exception to the 

 axial group of the Tangkul country. 



16. This will be a favourable opportunity for a short digression to 

 Tipam group and consider the relations of these rocks with those 

 axials - to the north in the Assam coal-fields. Here as 



described by Mr. Mallet, we have a series, the Tipam group, older than the 

 coal-bearing rocks, the latter being of* presumably nummulitic age ; the 

 former in general characters agree very fairly well with what I have 

 classed as ' axials/ and are very possibly identifiable with them ; this 

 would be further proof, if proof were necessary, that the ' axials ' are 

 not of nummulitic age, and further assign a triassic age to the Tipam 

 rocks. 



17. The trappean intrusions are confined to the eastern portion of 



the Tangkul country, and, if we except variations 

 Serpentine intrusions. 



in texture, due to unequal rates of cooling, sub- 

 stantially all of but one kind. In describing these the words used in the 

 Manual of the Geology of India when treating of the serpentine rocks 

 of British Burma, may be transcribed almost verbally ; the rock which 

 occurs in dykes of varying sizes, the main axis of the intrusion forming 

 a band some mile or two in breadth which runs throughout the whole 

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