DESCRIPTION OF SECTIONS. 265 



have been smelted: there are large heaps of copper slag at Pain 

 Robert in Afghan territory; but the ore may have been gathered 

 from various other localities in the north-western continuation of 

 the range in Persia. (See the chapter dealing with economic 

 products.) 



At Roba't Koh, in addition to the large bosses, there are also 

 small dykes forming sometimes a perfect network of branching and 

 anastomosing veins. When examined under the microscope, they 

 are found to consist of the same minerals as the large bosses, but 

 the texture is finer and the structure more porphyritic, as is also the 

 case towards the edge of the greater intrusions and at their narrower 

 extremities. At the edges of the great intrusions and in the smaller 

 dykes, the igneous rock and the limestone with which it comes in 

 contact have reacted upon one another, causing much alteration, es- 

 pecially amongst the ferromagnesian silicates. The adjoining lime- 

 stone shows small veins and cracks full of epidote 



Contact effect. „.. . 



and the internal cavities 01 nummulites are tilled 

 with that mineral (spec. ^-f). The occurrence of epidote as a pro- 

 duct of contact metamorphism in limestones is uncommon, although 

 instances have been recorded from other regions. 1 



In addition to these dykes, the limestone at Rob£t Koh is trav- 

 ersed by others, usually of very small dimensions, whose mineralogical 

 constitution is quite different : these are highly basic or even ultra- 

 basic basalts. One dyke only 18 inches wide contains small crystals of 

 labradorite and augite in an almost perfectly isotropic groundmass. 

 Another specimen from a larger dyke is a limburgite consisting 

 of a very imperfectly crystalline base, with large 

 porphyritic crystals of augite, and perfectly 

 clear olivines, sometimes curiously intergrown. The remarkable fresh- 

 ness of the latter rock makes it appear as if it were newer than the 

 dioritic intrusions ; but I have not observed any instance of the one 



1 J. Roth, Chemische Geologie, Vol.1 (1879), p. 430; J. W. Judd, Propylites of the 

 Western Isles of Scotland. Quart. Journ. Geol. Soc, Vol. LIII (1890) ; A. Lacroix, Mineral- 

 ogie de la France, pp. 139., 152. 



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