Field-notes: No. 5-to accompany a Geological Sketch Map of Afghanistán and North-Eastern Khorassan, by C. L. GRIESBACH, C.I.E., Geological Survey of India. Afghanistán is a land of high mountain ranges and two great areas of steppes; about three-fourths of its drainage passes to the Indus and Physical characters. to the inland basin of the Helmund, and only the northern. portion, not much more than one-fourth of the entire area, belongs to the AraloCaspian depression. By far the most important of all the ranges of Afghanistán are the Hindu Kush and Koh-i-Bába chains of mountains, which connectedly Ranges. form the watershed of Afghanistán. The Hindu Kush has a north-east to south-west direction, and divides the drainage of the Oxus river from that of Chitral, Kafiristán, and Kabul; the range joins the Koh-i-Bába near the Shibar pass south-east of Bamián, and thence pursues a more or less east and west direction. The western prolongation of this chain forms the watershed between the Seistán drainage and the Hari Rúd (Tejénd) and is known under various local names. In Khorassan the same system of ranges continues, but has a north-west strike. The range or system of ranges which comes next in importance after the great Central Afghan watershed is the system of parallel ranges which forms more or less the political boundary between India and Afghanistán, namely, the chains amongst which the central portion is known on our maps as the Sulimán range, named after the highest point in the range-the Takht-i-Sulimán. Geographically all the parallel ranges, from the Afridi hills near Peshawar to the Búgti hills southwest of Dera Ghazi Khán, form one connected system of mountains. The entire intervening area between the Sulimán mountains and the great Afghan watershed is formed by a series of high chains with wide troughs between. They start in the Kabul district and gradually diverge as they are followed southwestwards to the Persian frontier. They are formed by a steep folds, at other The structure and origin of these ranges is very simple. series of anticlinals, often compressed into a narrow belt with points forming wide arches, and in some cases even plateaux. The drainage of Afghanistán belongs to three separate areas. The Indus basin receives the drainage which flows from the Hindu Kush, Kafiristán, the Sulimán range, and of the ground west of it. The streams which rise in the Búgti hills and part of Biluchistán also run into the Indus basin. Rivers. The Ghilzai country and the southern Hazarajat send forth streams, which drain into the inland basin of Seistán; the Helmund is the largest and most important of these rivers. The third drainage area is that of the Aralo-Caspian basin, to which the Oxus, the Balkh-áb, the Murgháb, and the Hari Rúd (Tejénd) belong. Of these consider able rivers only the Oxus reaches a defined lake basin, namely, the Aral sea; the remainder loose themselves in the sands and swamps of the Central Asian steppes. Work done in Afghan. istán. Nearly all the rivers of Afghanistán have had the same history. They date back to late miocene times, since which period they have scooped out deep gorges and valleys whilst the country was gradually being laid into great anticlinal folds. Consequently they have nearly all of them formed fine examples of transverse valleys, which belong to the most characteristic features of Persian or Afghan landscapes. As will be seen from the annexed map, the greater part of Afghanistán is geologically still a terra incognita. All the mountainous country from the Sulimán range to the Hazarajat including the Zhob valley, has never been visited by a geologist. The Upper Hari Rúd, the Firozkohi country, and a large portion of the Northern Hazarajat are unknown to us geologically. So is the Taimuni country and the valleys which descend from the Siah Koh. During the second Afghan campaign, 1880, I reconnoitred the route from our Indian frontier to the Helmund, including the country south-west of Quetta. Afterwards (in 1883) I had the good fortune to accompany the Takht-i-Sulimán expedition under General T. G. Kennedy, C.B., and so was able to visit the highest part of the Sulimán range, which I found to be a stratigraphical continuation of the hills west of Dera Ghazi Khan, which have been described by Dr. W. T. Blanford. Later on, in 1884, 1885, and 1886, I was attached to the Afghan Boundary Commission, and examined the entire west and northern frontier of Afghanistán, together with Eastern Khorassan and the greater part of Afghan Turkistán, and was able to reconnoitre one section from the Hindu Kúsh to India. The outlines of the geological results thus arrived at are laid down in my published "Field-notes" in the Records. In the following pages I intend to summarize these results shortly. The geological literature relating to Afghanistán is extremely limited. I have already given lists of previous authors on matters connected with the geology of Afghanistán in former papers; it would be superfluous to again review this literature, as I shall have to do that when fully discussing the geology of Afghanistán in my forthcoming report. The annexed table will show the formations met with in the examined area of Afghanistán and Khorassan and their distribution. Since the publication of my "Field-notes" in the Records, some of the leading fossils of several formations have been examined by Dr. F. Noetling, and in consequence the "Red grits" had to be separated from the jurassics, with the uppermost portion of which I had previously identified them, and they are now included in the neocomian. 'Mem. Geol. Surv., Vol. XVIII; Records Geol. Surv., Vol. XVII, pt. 4, p. 177; ib. Vol. XX, pt. 1, p. 18. General features. geological It will be seen that the older rocks (paleozoic and mesozoic) are met with chiefly along the great Central Asian watershed, the main axis of Afghanistán. Strips of these rocks occur also at a few localities north of the main axis, and some doubtful and unfossiliferous rock groups in the Kabul district may possibly also be of older date than cretaceous. The rest of Afghanistán is covered with a thick skin of cretaceous rocks, the upper beds of which are often found to rest unconformably on the underlying older mesozoic strata. Large areas on the western and northern margin of Afghanistán are covered by tertiary strata. The main axis itself with the country north of it is part of a regular system of flexures, closely compressed near the main axis, but gradually increasing in width towards the north until they become gently undulating waves and widely spread flats Structural outlines. towards the centre of the Turkomanian area. The A similar feature is observable on the Indian side of the great watershed. spurs which I crossed between Quetta and Kandahar not less than the ranges lying between the Hindu Kush and Peshawar together with the Sulimán range are nothing but portions of flexures, and it may be inferred therefore that all the highlands of the Hazarajat and Ghazni down to our frontier show much the same structure as the ranges north of the Afghan watershed. Central Asia and Persia. All the formations met with in Afghanistán are also found spread over the greater part of Central Asia. The main axis of Persia which forms geographically a continuation of the Afghan watershed, resembles the latter also in its geological structure. The paleozoic and older mesozoic rocks are only met with in strips near the main axis and are elsewhere hidden by cretaceous and tertiary formations. The latter cover by far the greatest area in Turkomania and Russian Turkistán, Bokhara, &c., and only along the eroded base of synclinals older rocks appear. (Mushketoff's Turkistán.) Carboniferous older rocks. and Beds with true carboniferous forms have been found from the Araxes in Armenia to Central Afghanistán. They form narrow strips at the base of the older mesozoics, and as such they have been traced in a more or less uninterrupted zone along the Central Asian watershed. In some places in Persia they overlie some strata which have yielded fossils of rather devonian than carboniferous aspect, and it is possible that perhaps the entire palæozoic series will be found to exist. The same rocks extend into Russian Turkistán, where they crop up from beneath the covering of mesozoic (chiefly cretaceous) formations. Limestones and shales which contain apparently the same fauna have long been known to exist in Kashmir 2 and the Himalayas, and it seems therefore probable that all these carboniferous "islands" belong to the same widely spread formation and have been deposited in the same continuous sea. The dark limestone with Productus of Robat-i-Pai near Herat is both palæontologically and lithologically identically the same as the Productuslimestone of Spiti and the Central Himalayas generally. 'Records, Vol. XIX, p. 236. 1 See Lydekker's Kashmir: Mem. Geol. Surv. India, Vol. XXII. |