504 J. Starlde Gardner — Relalive Ages of 



The most extensive Cretaceous Molluscan fauna of America that 

 I have seen illustrated is that of California. The fossils are from 

 four stages. The lowest or Shasta Group, held to be of the antiquity 

 of the Gault, contains a thoroughly Cretaceous, though meagre, list. 

 The next group above is the Chico, supposed to be equivalent to the 

 Chalk formation of Europe, containing besides 14 typically Creta- 

 ceous Cephalopoda, 6 Cretaceous Gnsteropods, and 6 bivalves. On 

 the other hand, it contains Aluria and 2 very Eocene-looking Gastero- 

 pods, Saydenia and Sycodes. The Martinez Group contains 4 

 Cephalopoda and 5 Aporrhaidee of Cretaceous aspect, with 2 or 3 

 apparently Tertiary forms. The last, or Tejon Group, contains no 

 Cretaceous mollusc whatever, but no less than 34 species which 

 have a definitely Eocene facies. 



Professor Marcou wrote that he considered all the supposed Cre- 

 taceous rocks of California to be Tertiary, but without going so far 

 as that, there can be no question about the Tejon GroujD, at least, 

 being of that age. 



We liave seen that we are not justified in considering a large 

 proportion of the Cretaceous rocks of Europe as synchronous with 

 those of England. Far less are we in a position to identify those 

 of America with any particular stages in England. The question 

 whether they can be properly classed as Cretaceous at all, is even 

 debateiible. A Cretaceous fauna must have some elements at least 

 which did not survive into the Tertiaries. Are we in a position to 

 say that Ammonites and their allies did not do so in some localities? 

 Mr. J. A. Lebour wrote to remind me some time since, thatD'Orbigny 

 many years ago found an Ammonite in the Tertiary Coal-bearing 

 rocks on the coast of Chili, together with some other Cretaceous 

 forms ; and Darwin also noticed their occurrence. Saporta has also 

 expressed the opinion that Ammonites, Baculites and Inocerami per- 

 sisted for a longer time in America than in Europe, and instances 

 that in France the chambered Cephalopods left the Cretaceous seas 

 to the south, long before they disappeared from the north. JBelemnites 

 have more than once been recorded from Tertiary rocks. Such 

 ■distinctively Cretaceous genera as Nautilus, Pleurotomaria and Tri- 

 gonia still survive, besides many fish, the sponges, Encrinites, and 

 many genera of Cretaceous Echinoderms, etc.^ We justly enough, at 

 the time, assumed that they became extinct at the close of the 



^ "Tour letter has of necessity, remained unanswered, for the question of the 

 relations of the Cretaceous and the Tertiary Echinoidean faunas is one 1 and Sladen are 

 still trying to investigate. Alex. Agassiz's statements regarding the alliances of the 

 deep-sea forms with those of the Cretaceous are diminishing in value in our eyes, and 

 the subject is still in too crude a condition for any satisfactory argument to be developed. 

 Take, for instance, the genus Saknia, the 'Tertiary and the recent species do not 

 belong to the same group of forms which characterize the Cretaceous ; and they 

 differ from the Secondary group, more than these differ amongst themselves. The 

 same holds good for the species of Cidaris. Certainly no Cretaceous species siirvives, 

 and I am not siu'e that any one is common to the Secondary and Tertiary faunas. 

 There are many genera of Corals that are common to the Cretaceous, Tertiary and 

 the recent seas ; but not any well-defined species. Unfortunately, the American 

 fossil faunas do not assist in the research. In fact, the break of marine life is vast, 

 and the only connexion is by some Forams and genera of Planta3. — i'. M. Duncan." 



