1897.] NATURAL SCIENCES OF PHILADELPHIA. 455 



pliocene deposits. The first of these predominate in all the outcrops 

 and are almost always covered by the others. The upper Permian, 

 P 3 or PT, attains a thickness of 100 m. and more. It is developed 

 in an uninterrupted series of marls, sandstones, conglomerates and 

 more rarely limestones. 



The predominance in the series of this or that deposit affords a 

 differentiation of the following horizons : 



A. Clay and marls with interstratified beds of limestone. 



B. Sands and conglomerates with subordinated marls. 



C. Marls and sands with subordinated sandstones. 



D. Sandstones and sands with subordinated marls. 



E. The same rocks with beds of limestones and conglomerates. 

 In all the sections the horizons B and C are the most defi- 

 nitely and best expressed. The horizon A is in most cases eroded. 

 The lower horizons are most frequently masked by slips and 

 detritus and are not very visible, except near the villages of Issady, 

 Barmina, and Wassilssoursk. The fauna is represented by numerous 

 conchifer mollusks of the group Anthracosidce, especially by the 

 genera Palueomutela, Oligodon and Palceoanodonta ; by rare gastero- 

 pods Esther la, Palceonlscidce, Ceratod us and Stegocephali. The plant 

 remains are generally badly preserved. 



The Jurassic and Volgian deposits cover in separated islets the 

 Permian series of the environs of Issady, Barmina and Wassilssoursk. 

 These are dark gray clays with subordinate beds of sand, conglomer- 

 ates and limestone. Their ages are referred to the Callovian, Kim- 

 meridgian and Volgian epochs. 



The Post-pliocene is represented by yellow loessoid clays enclosing 

 a few pebbles and crystalline rocks. 



Below Issady the Volga valley's right slope forms an enormous 

 curve, in the upper part of which are seen from the steamboat yellow 

 outcrops more frequently of loessoid clays (Q x ),gray outcrops of the 

 Jura (J) partly hidden by thickets, and below, the outcrops of 

 Permian (Tartarian) rocks (P 3 or PT). The Jura, which is of excep- 

 tional interest in this section, is unfortunately less visible to-day than 

 a few years ago, when Sibirtzew, in 1886, established the following 

 sequence : 



(1) Yellowish brown loessoid clay. 



(2) Dark green sandstone with Amelia mosquensis of the Volgian 

 horizon (horizon of Oxynoticeras catenulatuni). 



(3) Black bituminous clay without fossils. 



