394 Trof. S. Sjogren — Valleys of the Caucasus. 



of mountains, the peaks of which rise to a height of 8000 or 9000 

 feet. The main chain of the Caucasus, where it forms the southern 

 boundary of Daghestan, runs in a straight line W. 28° S., while the 

 northern ridge I have just spoken of forms a regular curve, branch- 

 ing off from the other at Barbalo-Dagh and joining it again at Dulty- 

 Dagh. (See Sketch-Map, p. 393.) 



The tract of country included between these two ridges is Inner 

 Daghestan. Outer Daghestan is the tract which lies on the outer 

 slope of the more northerly of the two ridges, and which therefore 

 looks towards the Terak Steppe on the N. and the Caspian Sea on 

 the N.E. Inner Daghestan may also be described as the basin of 

 the four rivers Koissu. Surrounded as it is on every side by lofty 

 mountains, this region would be altogether without an outlet for its 

 waters, had not the combined streams of Koissu, which after their 

 junction bear the name of Sulak, found a way to the Caspian Sea 

 through the defile which we are now considering. This narrow 

 gorge is the only channel for . the drainage of an area of nearly 

 5000 square miles. 



The physiographical character of these two regions. Inner and 

 Outer Daghestan, is very different. Outer Daghestan consists almost 

 entirely of Tertiary formations, Palgeogene (probably Eocene) clay- 

 slates and sandstones, Sarmatian limestones, etc. It is only in the 

 crests of the anticlinal folds that the Cretaceous rocks here and there 

 appear. The strata of this region lie in gentle gradients as a rule, 

 and there are no dips exceeding 45°. The slope towards the Terek 

 Steppe and the Caspian Sea consists of terrace-like plateaux or 

 undulating highlands of a mean height of some 1300 feet, only the 

 branches and outgrowths of the mountain-chain behind reaching a 

 greater elevation. 



The character of Inner Daghestan is altogether different. Here, 

 as Abich pointed out years ago, Tertiary formations are entirely 

 wanting. The fundamental rock is exclusively Cretaceous or Jurassic 

 with the exception of certain of the earliest Caucasian schists, the 

 age of which is as yet unknown. 



Inner Daghestan again may be divided into two sections, as I 

 have already suggested in my paper " Uebersicht der Geologie 

 Daghestans und des Terek-Gebietes." ^ The lower section consists 

 mainly of limestones and dolomites belonging to the youngest 

 Jurassic and oldest Cretaceous periods, i.e. Malm and Neocomian. 

 These formations form extensive and high-lying basin-like plateaux, 

 which often end in precipitous, almost perpendicular, cliffs. It is 

 only in the deep and narrow river-gorges that the schists of the 

 middle Jurassic period come into view. Among these plateaux are 

 that of Keher, lying between the Kara-Koissu and the Kumuch- 

 Koissu, and reaching its highest point in Turtji-Dagh (7950 feet) ; 

 that of Gunib between the Kara-Koissu and the Avarian Koissu, the 

 highest point of which reaches some 7770 feet ; and that of Kunsach 

 between the Avarian and the Andian Koissus, of which the Talokol 

 range (8980 feet) may be looked upon as the southern edge. The 

 1 Jahrbuch der k. k. geolog. Eeichsanstalt," vol. 39, p. 417 (1889). 



