392 W. F. Sume — Notes on Russian Qeology. 



strait of Miocene beds occupying the intervening space. The 

 borings have shown that starting from a point 80 miles N. of 

 Melitopol, the Tertiary beds attain their maximum thickness under 

 the Azoff Sea, really forming an immense synclinal basin, bordered 

 at one extreme by the Cretaceous and Archaean of the Don Cossack 

 country, and on the other by the Cretaceous, the Jurassic, and 

 Archgean of the Southern Crimea. 



From the above data it will now be possible to form some more 

 precise idea of the extent of the Central and South Russian Creta- 

 ceous Basin, and to trace its boundaries more sharply than has 

 hitherto been possible. "With that view I have visited many crucial 

 points, and have made a study of various Russian writings either ia 

 the original or from references in other pamphlets. 



(A map should be referred to in following out these conclusions :) 



1. One boundary of the Cretaceous basin is very closely connected 

 with the course of the Dnieper, the Chalk thinning out near Kieif, 

 as shown by boring, the Cenomanian and Albien (as shown by 

 Theophilaktoff) resting directly on Upper Jurassic W. of the Dnieper, 

 therefore Cretaceous deposits cannot be of great extent, and must 

 die away against the Archfean axis. 



2. The Jurassic beds follow the line of the Archaean axis towards 

 the S.E., the Cretaceous beds being thus limited to the N. The out- 

 crop of these beds therefore bends sharply to the E. passing S. of 

 Poltava, and resting directly (both Cenomanian and Senonio-Turo- 

 nian) on the Upper Jurassic beds at Izium, Kamenka, and Sviati- 

 Gori (Gourov and personal obs.) Borings also lead to the conclusion 

 that the Jurassic beds are developed in the N. of the Ekaterinoslav 

 Government to an extent not previously imagined. 



3. The boundary then successively rests on Permian (near Bach- 

 mut) and on Carboniferous parallel to the S. bank of the River 

 Donetz before it takes a bend to the E. From this point the 

 Cretaceous expands in the Don Cossack country, sending off an arm, 

 which, passing under the Tertiaries of Taurida, reappears in the 

 Cretaceous hills of S. Crimea (Golovkinski). The main mass passes 

 southward towards the Caucasus, disappearing under the Aralo- 

 Caspian strata that occupy the space between the Azoff and Caspian 

 Seas. Their boundary is probably somewhat N. of the main 

 Caucasus range, as Neocomian fossils have been met with both at 

 Kislovodsk and Piatigorsk. 



It would be scarcely right to include in this paper the deposits 

 containing Inoc. Cripsii and Belem. mucronata, which occur in the 

 S. Caucasus and in Armenia and Daghestan, especially as these 

 present the characters of the Southern Cretaceous type. With this 

 limitation, the extension of the beds to the W. may be next studied, 

 and in the provinces of Voronesh, Simbirsk, and Saratov, as also iu 

 the Obschei Sirt Hills, white chalk (apparently closely related to the 

 Senonio-Turonian ah-eady mentioned) is developed on an immense 

 scale. Murchison has shown that near Indovistye, W. of Voronesh, 

 the W. chalk is only 20 feet thick and immediately overlaps the 

 Devonian, 100 feet of Greensand (Cenomanian) occurring below. 



