412 PROCEEDINGS OF THE ACADEMY OF [1897. 



borne in mind that the westward flowing streams usually have their 

 origin in extensive marshes and bogs lying in the elevated parts of 

 the longitudinal valleys, and covering many square wersts 1 or kilo- 

 meters. The first part of their course, or that more or less on the 

 line of the meridian north or south, is usually rapid and tumultuous. 

 In their middle course they take a sudden change in a direction at 

 right angles to their final course and descending with the same 

 rapidity cut through gorges ten wersts or so in length with abrupt 

 and sometimes vertical walls 100 meters and more in height. 



Having passed the westernmost rocky barrier the rivers flow 

 sluggishly through large alluvial valleys in which rock in place is 

 rarely seen, and the affluents of the larger streams are few and small. 

 These valleys are filled with the remains of ancient river and lake 

 beds, and show distinctly alluvial terraces. 



Having brought the section to the lower Permian spotted lime- 

 stones and dolomites the further journey east reveals a series to 

 which the name Permo-Carbonic has been given. 2 



This band separating the two groups is divided into an upper or 

 calcareo-dolomitic, and a lower member called the horizon of Artiusk. 

 This latter contains sandstones, limestones, marls and various 

 schists. Karpinsky, Kratow and Tschernischew have shown that 

 it is characterized by original ammonitides of great interest since 

 the discovery of similar forms at Darvas in Sicily, in Texas, and 

 other places. It contains brachiopods also, of which the study has 

 established the connection of the different subdivisions of the Pro- 

 ductus limestone of the salt range with the paleozoic deposits of the 

 Oural. 



The Carbonic of the South Oural consists exclusively of three 

 sections of limestones each, and especially the uppermost, character- 

 ized by an abundant fauna. 



The Devonic is also represented here in all of its three sections, 

 of which the lower is much the most interesting, both because to it 

 is attributed the rocks forming the highest chains of the Ourals, and 

 because it is therefore the real crux in the geology of these mountains 

 which is destined to give rise to a voluminous literature, and remain 

 a moot point among geologists for many years to come. The middle 

 division of the Devonic is also of interest as frequently containing a 



1 Eleven kilometers are reckoned equal to ten wersts. 



2 It would have been more in conformity with usuge had the name been 

 Carbono-Permian. 



