CORRELATION OF TENDAGURU SERIES 277 



Correlations on basis of marine ifiverteb rates. — A careful reading of 

 these most interesting memoirs makes it evident that all of the workers 

 are finally dependent in their correlations on the evidence presented by 

 the ammonites. These are determined by Zwierzycki,** who regards those 

 of the Trigonia schwarzi zone as a typical Mediterranean lower and 

 middle Neocomian assemblage. The majority of the forms in other 

 regions, he states, are at home in the upper Yalanginian and in the 

 Hauterivian. Only the forms of Crioceras and Hamulina may be indica- 

 tive of a higher zone, the Barremian. He also distinctly points out that 

 the forms occurring in Europe are there restricted to distinct horizons, 

 but that in the Tendaguru region they are apparently associated. 



The Trigonia smeei zone Zwierzycki also regards as having a mixed 

 fauna, with nine species that elsewhere again hold two horizons. Haplo- 

 ceras elimatum ranges from the upper Kinmieridge into the Tithonian, 

 while Phylloceras silesiacum is restricted to the Tithonian (Stromberg). 

 Perisphinctes hleicheri is also indicative of Tithonian. Haploceras Jcohelli 

 is of upper Kimmeridge age. From this evidence the author concludes 

 that the T. smeei zone is of about the time of the upper Kimmeridge and 

 Tithonian, or, in other words, at the top of the Jurassic. ( See Buckman's 

 views beyond.) In this connection it should not be forgotten that above 

 the Kimmeridge follows the Portlandian and Purbeckian (at least 1,000 

 feet thick in England and thicker on the continent), and, further, that 

 the position of the Tithonian has long been under discussion, and even 

 though the majority of stratigraphers refer it to the Jurassic, others 

 regard it as of Lower Cretaceous time. Kayser states that about a dozen 

 of its species pass upward, and that the succession of its ammonite beds 

 leads imperceptibly into the Lower Cretaceous. Therefore the Tithonian 

 species of the T. smeei zone may have been actually living in Lower Cre- 

 taceous time. 



The N"erinea zone, Zwierzycki states, is difficult to correlate on the basis 

 of cephalopods alone, because of the six species present the only guide is 

 Perisphinctes sparsiplicatus, a form from the Katrol formation of India. 

 He adds that if this species, founded on a single specimen, is from the 

 lower Katrol, it may mean that the age is Oxford, and if upper Katrol, 

 then the time is Kimmeridge. Because the ISTerinea zone underlies the 

 middle dinosaur beds, he is inclined to refer the former to the Oxfordian. 

 However, he is not certain about this, and adds, "At least it is older than 

 Upper Kimmeridge." Accordingly he regards the middle dinosaur zone 



** J. Zwierzycki : Wissenschaftliche Ergebnisse, etcetera, part iii, pp. 83-87. 



