STRATIGRAPH1CAL ELEMENTS: CRYSTALLINES, ETC. 75 



(5) Trap dykes intrusive among (/), (2), C?)> and M- 

 A few basic trap dykes are known in Hazara. They are always 

 noncrystalline, and may be generally described 

 Generalities. ^ plagioclase -. au gi te rocks or dolerites. No- 



where that I am acquainted with is there any outflow of the basic rock 

 in the form of a subaerial lava stream, such as those which occur 

 abundantly in the Lower Himalaya, e.g., north of the Dudatoli massif. 

 (Rec. G. S. of I., Vol. XXI, pt. 1, 1888). On the contrary, the rock is 

 everywhere a dyke rock ; and, if lava streams were ever formed in 

 connection with them, all traces of them have since been swept away 

 by denudation. 



The variations which occur in the mineral composition of the rock 

 at different localities seem to be purely due to 



Structure and varia- the effect of me tamorphism of the original plagio- 

 tions. r 010 



clase-augite rock. The rock varies in texture 



from a fairly coarse dolerite to a fine aphanitic rock, the colour from 



mottled greenish-black and white to dark greenish-black. Foliated 



varieties with change of the rock into a hornblende-schist occur at 



the edges of dykes cutting through the gneissose-granite of the 



Indus river. Examples will be given presently. A columnar variety 



of trap with five-sided columns occurs due west of Shingli on the 



ridge. 



The basic traps of Hazara do not occupy any large surface of the 



country ; but they are generally found in the 



Habit of the rock. \ J a A \ li 11 1 



form of narrow bands or dykes roughly parallel 



to the foliation of the intruded rock, which latter, from the fact that 



in certain places the dykes cut across both the schistose series and 



the gneissose-granite intrusions, and also send off small veins into 



them, must be judged to be older than the traps. A few examples 



may here be given. At the junction of the Shal N. with the Indus 



river, Black Mountain, the trap would appear certainly to be 



younger than the rock among which it is found, because it cuts 



through the foliated schists and also through the gneissose-granite 



( 75 ) 



