FK. VON HATTER CONGEBIAN STRATA. 23 



3-83 near Carthagena, and 3-77 near Malaga, — these numbers repre- 

 senting an average proportion of 3" 78. 



The Molluscan fauna of the Caspian Sea is remarkable for its ex- 

 treme scarcity of genera and species, and for the predominance of 

 peculiar forms of Cardium (the types of the subgenera Adacna, Mono- 

 dacna, and Didacna in Prof. Eichwald's ' Fauna Caspio-Caucasica'), 

 as also by its characteristic forms of Dreissena and Mytilus. Pallas 

 long ago pointed out the far greater extent of the Caspian in ancient 

 times, and its former connexion with the Aral and the Black Sea ; 

 and his views have been fully corroborated by subsequent observers, 

 especially by Sir R. I. Murchison, Count von Keyserling, and M. de 

 Verneuil, in ' Russia and the Ural Mountains* ' 



If we take into consideration the Tertiaries of the plains of the 

 Danube and its affluents, as far as they fall within the limits of 

 the Austrian Empire, beginning with the most thoroughly known 

 among them (namely, those of the Vienna basin), an impartial ob- 

 server will scarcely have any doubt as to the analogy of the fauna 

 preserved in our Inzersdorf or Congerian plastic clay (" Tegel ") with 

 the recent Aralo-Caspian fauna. The deposits just mentioned are 

 very poor in species, but contain very numerous individuals of Con- 

 geries (Dreissence), together with plenty of Cardia (some of them 

 scarcely distinct from Prof. Eichwald's species) a.n.& Paludince, of which 

 one has been identified by M. Frauenfeld * with the recent Paludina 

 pusilla, Eichw. Nevertheless the fauna of the Inzersdorf strata is 

 distinct from that of the Aralo-Caspian beds by the presence of 

 Melanopsis and other species, connecting them with the other Mio- 

 cene deposits of Europe. 



Prof. Edw. Suess was the first who succeeded in fixing the true 

 position of these Inzersdorf Clays, in relation to the rest of the de- 

 posits filling up the Vienna basin. This distinguished palaeonto- 

 logist has proved them to be of newer date than the whole of the 

 marine strata, and to have been deposited above them, in the lowest 

 localities of the basin, at a period when the level of the ancient 

 Miocene sea had already notably decreased, and the per-centage of salt 

 in its water had nearly fallen down to zero by the influx of fresh 

 water. This observation is quite concordant with the fact sig- 

 nalized by the celebrated authors of the above-mentioned work on 

 Russia, — of the Aralo-Caspian freshwater deposits resting on marino 

 Miocene beds ; while Capt. Spratt expressly asserts that his fresh- 

 water strata rest immediately on Eocene deposits. 



The extensive range of the Inzersdorf Clays within the Vienna 

 basin, their occurrence in its lowest portions, the appearance of their 

 organic remains at very many isolated localities (as proved by local 

 occurrences of the characteristic Melanopsis Martiniana, enumerated 

 in Dr. Homes's 'Tertiary Mollusca of the Vienna basin'), leave 

 no doubt of their having been deposited within this basin in an 

 extensive and continuous lake, the diameter of which from S.S.E. 

 to N.N.W. (from Oedenburg in Western Hungary, to Gaya in Mo- 

 ravia) has a length of 20 Austrian (about 90 English) miles. The 



* Homes, Die fossilen Molluskcn cles Tertiarbecken von Wien, i. p. 587. 



d2 



