CRYSTALLINE SERIES. 



15 



to Ammk at the foot of a high crest, which rises in the Arnluk peak to 7,790 feet ; 

 it runs from that locality always at the southern slope of the main crest of the Siah 

 Koh to the Gachao peaks, south-east of whioh it crops out in the valley of the Surkh- 

 ab (river). It may be seen all along the scarp on the left side of the river as far as 

 the Doronta gorge of the Kabul river, and thence strikes across into the hills which 

 form the Besiid and Krinar ranges. This belt of limestone beds is economically 

 important on account of the rubies which are found within it. They occur in a 

 highly crystalline, coarse marble, which oontains mica as accessory mineral ; garnets 

 and spinel occur with rubies throughout this belt, but at a few spots are accumulated 

 in nests as it were, and then the entire rock is tinted a pink colour with the minute 

 crystals of these minerals. With the schistose beds below the belt is closely connected 

 both stratigvaphically and mineralogically, several thin beds of crystalline limestone 

 being seen interbedded with the mica schist below. 



" South-west of the Doronta gorge, near Kala-i-Sher, the section through the 

 limestone is well exposed in most of the small ravines which cut through the scarp. 

 I noticed that resting on the base of metamorphic schists are highly crystalline lime- 

 stone beds in flags, with shaly partings : the limestone, though crystalline, has pre- 

 served its stratified structure perfectly. It is dotted with small rusty spots, which, I 

 believe, owe their origin to decomposed garnets, which in other localities are common 

 throughout the belt. Besides this it is h'ghly characteristic of these limestone 

 beds that white mica in small leaflets occurs in profusion along the plane of 

 stratification throughout. 



"Some distance higher in the section near Kala«i Sher I observed some 40-50 

 feet of this limestone band almost unaltered and formed by dark grey hard limestone 

 in which indistinot fossil impressions are visible with many fragments of arinoids. 

 The whole appearance of the limestone reminded me of much the dark crinoid 

 limestone of the Hindu Kush, which also is associated with metamorphic strata— a 

 limestone which I have placed in the carboniferous system. 



" The beds above this fossiliferous limestone are much more altered, and are in 

 fact converted into very fine white marble, fine grained and almost structureless. 

 It is now being worked as a statuary marble by the Amir's people. Even in this 

 marble isolated leaflets of mica are discernible, whilst higher up in the section the 

 marble becomes very coarsely crystalline, which then contains much mica. 



" The entire thickness of the limestone zone cannot be less than about 3,000 feet 

 in this section." 



It would appear from this that the ruby-bearing limestone is closely 

 associated in age with the crinoid limestone of Kala-i-Sher and if we 

 accept Mr. Griesbach's conclusions, we must follow him, not perhaps in 

 referring the beds to the Carboniferous system but in basing an estimate 

 of their age on that of the crinoids. Unfortunately, these are not 

 sufficiently characteristic for determination ; possibly, however, the rock 

 corresponds to the crinoid limestone of the Waghzar valley in Ghorband 



