72 



HAYDEN : GEOLOGY OF NORTHERN AFGHANISTAN. 



On the east of the Kotal-i-Hajigak down to Kharzar, the prevailing 



rock is slate. At Kharzar this is replaced by a 

 Kharzar and Siah-sang. . . 



great thickness or quart zite, which has the shining 



black surface so commonly found on arenaceous rocks weathering under 

 desert conditions ; it exactly resembles hematite, and at first sight one 

 is inclined to refer all the tall black masses of rock standing out so 

 conspicuously in the Helmand valley to this mineral ; but I examined 

 a large number of outcrops and in not a single case did those east of the 

 Kotal-i-Hajigak prove to be iron-ore. 



From Kharzar to Siah-sang there is a monotonous repetition of the 

 same rocks — quartzite and slate — all the way. For some miles below Siah- 

 sang the conditions continue much the same, but towards the Helmand 

 signs of contact-metamorphism begin to be apparent; the slates become 

 silky at first, then are phyllites, and subsequently contain considerable 

 quantities of chiastolite. Near the river they are 



^Gardan' Dtoal** associated with grey schistose limestone and calc- 

 schist, and on the east of the river between 

 Gardan Diwal and Jaokul, the series has become definitely a highly 

 metamorphic one composed of schist and crvstalline limestone. The 

 limestone is very conspicuous, and forms a belt nearly 1,000 feet broad. 

 It is a grey saccharoid rock with au gen of quartz and calcile, which may, 

 perhaps, be the remains of fossils ; some of the fragments of quartz, 

 however, are very like included pebbles. Part of this limestone belt 

 consists of white marble with graphite. The metamorphism is due to 

 biotite-granite which occurs in some quantity to the south of Jaokul. 



Between Siah-sang and the Helmand, the prevailing dip is south- 

 erly, but northerly dips have also been noticed over considerable dis- 

 tances, and it is evident that the whole series has been repeatedly folded. 

 To the south of Gardan Diwal, on the right bank of the river, and 

 again in the valley of the stream which passes in front of the Jaokul 

 caravansarai, the slates are chiefly vertical. 



To the south-east of Jaokul, similar rocks extend to the Kotal-i- 

 Unai, which lies on the divide between the Kabul and Helmand river 



