i8y5. OCEAN DEPOSITS, ANCIENT AND MODERN. 387 



known from the Upper Cretaceous, and still existing, shows that but 

 few extend beyond the 1,000-fathom line, yet at these consider- 

 able depths Area has been found 7 times, Lima 4, Lyonsia 3, Leda 2, 

 Nticnla 2, Pecten 2, Pectnnculits 1, Venus i, Teredo i, and Modiola i. At 

 a range not exceeding 600, but deeper than 300 fathoms, Anomia, 

 Lucina, Tellina, and Cardium have also been obtained. The fine- 

 shelled forms, such as Necera and Callocavdia, are decidedly deep-sea in 

 their characters ; but should they have existed during Cretaceous 

 time, it is more than probable that, owing to the delicacy of their 

 tests, they would not have been preserved. 



3. What is the character of the distribution of the Mollusca in 

 Cretaceous times, and is there any general resemblance to the 

 sequences above noted ? 



We have in Germany two regions serving as a basis for com- 

 parison with modern conditions : the shore-line of the South German 

 Continent on the one hand, and on the other the Rugen Chalk, which 

 must have occupied a fairly central position in the Chalk Ocean. 

 Taking for the purpose of analysis those strata of the first area which 

 correspond in age to our Upper Chalk, we find the Gastropoda repre- 

 sented by ninety-six species, the principal genera having the following 

 specific development : 13 species of Ftisus, 12 of Trochus, 11 of Rostel- 

 laria, 8 of Tiirritella, 7 of Cerithinm, 6 of Volnta, 6 of Dentalium, 4 of 

 Acmaa, and 4 of Strombus. Similarly, the Pelecypoda are represented 

 by 186 species, distributed as follows among the predominant genera : 

 Pecten 30, Area 16, Lima and Venus each 13, Inocevamns 12, Nucnla 10, 

 Avicula and Cardium each 8, Mytilus 7, Corbula and Pholadomya 

 each 6, Cavdita and Peduncuhis each 5 species. 



In favour of the idea that the Chalk of Riigen was deposited in 

 far deeper seas than the above, there is the following evidence : in it 

 are found only 2 genera of Gastropoda, viz., Trochus i species, and 

 Nerita i species; 2 species of Dimyaria, both Area; 19 species of 

 Monomyaria distributed between the ubiquitous genera Inoeeramus, 

 Pecten, and Lima ; also i species of Gervillia, which, commencing in 

 the lowest beds of the Upper Cretaceous and continuing to the 

 highest, has not only a wide range in time, but also an extended one 

 in area, occurring, as it does, in Bohemia, Saxony, Schleswig, the 

 Hartz, and Aix-la-Chapelle. It is surely significant that every one of 

 the comparable genera found at Riigen is of a type known to exist 

 in modern seas at a depth of over 1,000 fathoms, and that all the 

 littoral forms so abundant on the shore-line of the South German 

 continent should have absolutely and entirely disappeared. 



Again, from a geographical point of view, some marked distinc- 

 tions are to be observed. Leaving the Aix-la-Chapelle deposits out 

 of account, we find that of twenty-four Gastropod genera a gradual 

 variation takes place; 18 occur in Bohemia, 13 in Westphalia, 10 in 

 Schleswig, and 6 in the Hartz. On the other hand, the Dimyaria take 

 almost an exactly opposite course, there being 21 in the Hartz, 20 



