THK T1UASSIC SYS'IKM 379 



that sea was established across Bavaria, and perhaps also through 

 Silesia to the east of the Bohemian Highlands. With regard to 

 Russia little evidence is available, because any Triassic rocks which 

 may exist in the western and central parts of that country are 

 concealed beneath a thick cover of Jurassic and Cretaceous strata. 

 In the Astrakan province, however, the Bogdo Mountains are 

 r;i]i]icd by outliers of a limestone which is believed to be of Mus- 

 chelkalk age, and beds belonging to the Upper Trias occur in the 

 Crimea, so that it is very likely that the Southern Sea spread over 

 a large part of Southern Russia during Muschelkalk time. 



We have seen that a great thickness of rock-material was 

 accumulated in this Southern Sea, and that as time went on the 

 deposits formed therein became, at any rate in some parts, more 

 and more calcareous. At the same time it does not seem to have 

 been a deep sea, for apart from Molluscan shells (chiefly Lamelli- 

 braucha and Gastropods), the principal components of the lime- 

 stones are calcareous algae (Diplopora and Gyroporella), which at 

 the present day do not flourish much below 150 fathoms. Hence, 

 to account for the much greater mass of deposit in Austro- Alpine 

 region, about 5000 feet as compared with 1000 in Germany, \ve 

 must suppose that subsidence was more continuous in the southern 

 than in the northern region. 



The truth of this inference is confirmed by a consideration of 

 the area where the German and Austrian fades of the Trias approach 

 most nearly to one another. Between the Schwartzwald and 

 Bohemia the German Keuper dips southward under the Jurassic 

 strata of the great Danubian plain ; while south of this plain, and 

 cropping out from below the same Jurassic and Cretaceous rocks, 

 are the highest members of the Austrian Trias, extending from the 

 Vorarlberg to the Salzburg district. The breadth of this interven- 

 ing tract, which conceals the passage of one facies into the other, 

 between Tubingen and the Vorarlberg is only 100 miles. 



There is no good reason for supposing that this tract conceals a 

 ridge of Paheozoie rock, which could have formed a land-barrier 

 between the two regions ; it is much more probable that the one 

 facies passes into the other with a comparatively rapid change, and 

 the facts can be explained on the supposition that the crust- 

 movements were of a counterpoising nature, the southern region 

 continuing to subside while the northern at the beginning of 

 Keuper time underwent a slight uplift with a north-west tilt, so 

 that while the uplift was sufficient to cut off the northern area 

 from the Southern Sea the inland waters were able to extend 

 themselves farther west than those of the Muschelkalk had done. 



In this manner was produced the great salt lake or inland 



