TF. F. Hume — Notes on Russian Geology. 393 



150 m. to the E. at Volsk on the Volga the chalk is 200 feet thick 

 containing Belemnites ? possibly Belemnitella, Pecten (like quinque' 

 costata). There is, however, a more general tendency for the 

 Cretaceous beds to become clayey or sandy in the two Governments 

 of Simbirsk and Saratov. The former condition prevails in the 

 Simbirsk, the latter in the Saratov Government. Thus, at the town 

 of Saratoff itself, Murchison had previously shown that the Upper 

 Cretaceous beds, include white, grey, and bluish marls containing 

 Belemnitella mucronata and Pecten cretosus. In the N. of the 

 Simbirsk Government Neocomian and Aptien beds occur, and only 

 the S. portion of the Government is occupied by the Upper 

 Cretaceous. Finally, Sintzoff has shown that the Cretaceous is 

 represented by soft Chalk and Chalk Marls in the Obschei Sirt, a 

 band of hills in the neighbourhood of Orenburg. The white Chalk 

 at Uralsk here contains Belem. mucronata, and Echinocorys ovata, 

 thus probably forming the E. part of the great central basin. On 

 the Siberian side of the E. Oural these beds sink beneath the 

 Tertiary of the Kirghese steppes. It will be advisable to give the 

 succession in a few typical localities in these Western Governments, 

 so that a clear idea may be formed of their general characteristics. 



The succession near Simbirsk (Yasikoff) is as follows (see 

 Murchison). 



I. (1) White Chalk, with courses of chert, occasional deposits of 

 tripoli, and masses of ferruginous ochre. (2) Chalk Marl with 

 bands of chloritic Chalk, in lower parts of which occur Inoc. Cuvieri, 

 Pel. mucronata, and Zoophytes. (3) Marls with phosphatic nodules. 

 Total above 250 feet. 



In the Upper beds occur Tereb. carnea, T. subrotunda, Micraster 

 coranguinum, Plngiostoma Hoperi, Pel. mucronata, Scaphites (squalis, 

 with Zoophytes, Crustaceee, and teeth and vertebrae of fishes. 



II. Below these occur 300 feet of variegated clays, containing 

 Amm consobrinus (Upper Neocomian). Their position reminds us of 

 similar clays below Greensand at Sviati Gori. 



III. The base is formed by the Besonov and Simbirsk clays, contain- 

 ing such typical forms as Inoc. concentriciis, and Hoplites Deshayesii. 



Lower down the Volga, at Kwalynsk, Chalk 200 feet thick 

 occurs, resting directly on Jurassic sands and shales. 



The characters of the strata at Volsk have been mentioned on the 

 previous page. 



Still following the Volga, we arrive at the town of Saratov, with 

 the beds well exposed on its shores. There is here a lithological 

 difference, and in Fig. 344 (Murchison's " Eussia and the Urals ") 

 the succession is given as follows : — 1. Grey clays with Ostrea 

 vesicularis. 2. White, grey, and bluish marls with Pel. mucronata 

 and Pecten cretosus. 3. Sponge-bearing strata. 4. Calcareous sand- 

 stones, with Terebratula and Ostrea lateralis. Below these come 

 Jurassic beds. 



100 miles to the S. at Kamischine, Inostranzoff mentions 

 Neocomian and Aptien zones, whilst further S. at Bielaiaglina 

 (white clays) pure white Chalk occurs containing Terebratula carnea. 



