24 



HAYDEN : GEOLOGY OF NORTHERN AFGHANISTAN. 



follows approximately the crest of an anticline, and the Kalu series is 

 found on both sides of the river. 



Hajigak Limestone and Hematite. 



The graphitic slates in the neighbourhood of Kalu (Plate 4) are 

 apparently overlain by a thick bed of hematite, which can be seen for 

 miles capping the high ridge which runs north-eastwards towards 

 Ghorband. On the southern tlanks of this ridge, the hematite is over- 

 lain by slate which, in turn, is overlain by grey limestone with calcite 

 veins and numerous small crystals of hematite ; this is associated with a 

 fossiliferous, black thin-bedded limestone. An outcrop of the latter 

 limestone is seen at the edge of the road, just at the foot of the Hajigak 

 pass, where a stream flows down from the north. Fossils are numerous 

 in this small outcrop; they are chiefly brachiopods including Sjririfer 

 cf. V crneuilii Murch., Stroplialosia sp. and Rhyncltonella sp. The 

 grey limestone seen higher up the hill-side contains corals, including 

 the genera Zaphrentis and Syringojjora ; with these I found a few 

 fragmentary brachiopods, similar to those occurring in the higher 

 beds, and part of the thorax of a trilobite. The black limestone is 

 probably Devonian and thus gives us a datum line to work from. 1 

 At the same time, the hematite bed is a most characteristic horizon 

 and, being readily recognised where the overlying limestone is either 

 unfossiliferous or metamorphosed, is an invaluable guide in the eluci- 

 dation of the complicated structure of Ghorband and the Hindu Kush. 2 



1 Since writing the above, I have heard from Mr. P. R. Cowper Reed, who has 

 kindly examined the specimens for me, that ths fossils of the black limestone are Upper 

 Devonian and those from the grey limestone Lower Carboniferous. A description cf 

 them, by Mr. Cowper Reed, will shortly be published in the Records of the Geologi- 

 cal Survey. 



2 In view of the presence of hematite associated with Devonian limestone in the 

 Koh-i-Baba it is interesting to note that the magnetite beds of Alt. Magnitna'ia in the 

 Southern Urals are regarded by Nicolaew as derived from Devonian deposits. He 

 believes the magnetite to have arisen from the alteration, by eruptive rocks, of 

 hematite or spathic iron the oiigin of which, he further suggests, may perhaps be 

 sought in the action of ferruginous or siliceous solutions on a limestone, probably of 

 Devonian age (22, 670;. 



