414 PROCEEDINGS OF THE ACADEMY OF [1897. 



Zigalga to Avniar transversely to the direction of the Zigalga and 

 of the Bakti and crossing the rivers Yourezan, Avniar, and Bieleia. 

 This section shows the principal mass of the bed of quartzose sand- 

 stone D} g between two schistose beds of which the lower rests 

 directly on the oldest limestones Dl c of characteristic fauna. The 

 predominant rock of the lower schistose bed is a black sericitic 

 schist reflecting on its steel-gray surface, sometimes a silky lustre. 

 Quite often is observed the passage of these schists into micaceous 

 and chloritic varieties, very rich in magnetite and hematite. Taking 

 up quartz these schists pass into micaceous and talcose quartzites. 

 In places the black argillaceous schist shows inclusions of large 

 pyrite crystals, and pseudomorphs of pyrite in limonite." 



'This black schist is associated in the lower part of the bed D} g 

 with a serecitic schist nearly of the same composition as the black, 

 but poorer in carbonaceous matter and consequently of a lighter 

 shade.' 



' After a certain amount of practice it is easy to distinguish the 

 lower schists, situated under the horizon of quartzites and sandstones, 

 from the schists which surmount this horizon. The latter of very 

 variable color, structure, and composition never have this reflexion 

 on the plane surface but they pass also, though very rarely, and in 

 exceptional cases, into chloritic and ottrelitic schists. Their color, 

 sometimes banded, varies between dark gray almost black, yellowish, 

 greenish, and reddish gray. Marly sandstone, marls, and limestones 

 occupy a second rank in the bed Dl g.' 



'A series of rocks Dl g separates, as we have said, two beds of 

 limestone essentially different from a paleontological point of view. 

 The upper limestones D^ g of which the type is developed in the 

 Yourezan valley encloses subordinate beds of argillaceous schists 

 and marly sandstones. Their paleontological character is described 

 in the paper, ' Die Fauna des unteren Devon am Westabhange des 

 Ural,' by Th. Tschernischew. This horizon is especially character- 

 istic by its abundance of Leperditia Barboti, small trilobites of the 

 genus Cyphaspis, Pentamerus fasciculatus, Pentamerus baschkiricus, 

 remains of conchifers Conocardium erenatum, Buchiola sexcostata 

 and other forms.' 



'The lower limestones Dj c capped by the bed D\ g and often 

 found between metamorphic rocks (as in the upper course of the 

 Bieleia), are distinguished by their lighter tints, and a marble 

 structure. Their fauna described in the above work by Tschernis- 



