184,5.] 



515 



in some parts having its hornblende replaced by diallage, or its 

 felspar paste by a magnesian one, passes gradually into diallage 

 rock and serpentine, and rises in dykes, or is laid bare in the 

 bottom of deep valleys, at several points between this and a Koord 

 village about five miles to the north-east. 



The elevated peninsula formed by the Tigris, which is crossed 

 '^'by the road to Arghaneh Maden, is composed almost entirely of 

 ophiolite, or of a variety of serpentine and diallage rock. These 

 are seen immediately on the western side of the river, which is 

 here crossed by a stone bridge. The colour of the rocks is com- 

 monly bottle green ; but hardly a square yard of it is homogeneous, 

 so frequent are the changes in the material. The cracks and 

 fissures are filled with precious serpentine, with asbestos, and 

 other minerals, chiefly of silicates of magnesia. The greater por- 

 tion of the rock, howevei', is characterised by interspersed foliated 

 crystals of diallage, sometimes as large as the palm of the hand, 

 which reflects so brightly the sun's rays as to be generally taken by 

 the natives for a species of silver. About a mile further to the 

 north, at the opening of a valley which 

 runs up from the Tigris in the direction 

 of Maden, are found some very singular 

 conical mounds and hills, which render 

 probable the eruptive origin of the ser- 

 pentines. Their summits are formed by 

 a crest of tilted strata of limestone or shale, supported by a mass 

 of sei-pentine or diallage rock, which has been much decomposed 

 by exposure, and is even sometimes so much worn that the cap of 

 harder stone projects from its base, as if nicely balanced upon it 

 by art. 



On the road to the mines, are passed strata of finely laminated 

 shales, which are, here and there, interrupted by dykes or masses 

 of diallage rock, and frequently become allied to jasper. 



The serpentine is laid bare at Arghaneh Maden, in the valley of 



Mining Distkict of Arghaneh-Maden. 



The dotted pavts in this diagram represent diallage rock, the crossed lines an 

 irregular mass of sulphuret of iron and copper in whicli the mines are situated, and 

 the remainder of the marks, limestones, and metamorphic slates of various periods. 



the Tigris, and in the ravine formed by a rivulet which pours in 

 its tribute close below the town. The rock is generally full of 

 diallage, and contains the other magnesian minerals before de- 

 scribed. From its being intersected in all directions by fissures 



