COMPARISON OF FAUNAS. 400 



tion of Aucella? described by Dr White.* This negative evidence coin- 

 cides with the facts brought to Ught by the examination of the Am- 

 monitinae of Alaska and those of mount Jura and the Black hills. All 

 the fossils so far described from these localities belong to faunas older 

 than those of Europe in which Aucella occurs. 



The fauna of the Black hills, acknowledged to be Jurassic by every 

 one but Whiteaves, is in part apparently synchronous with that of the 

 Aleutian islands and Alaska, as described by Eichw^ald and Grewingk. 

 The differences between the Upper Jura fossils in both are simply such 

 as might occur between any two different basins situated in approxi- 

 mately contemporaneous faunas. This parallelism and the additional 

 negative evidence of the collections of Grewingk and Dall led me to sus- 

 pect that Eichwald might possibly be w^rong in stating that the Aucellse 

 of Alaska were associated with the Ammonitina^ of the Upper Jura w^hich 

 he describes. 



The faunas of Alaska, the Black hills, and Aurora, Wyoming, corre- 

 spond in part, at least, so far as the marine invertebrata are concerned, 

 to that part of the Jura known in Russia as the zone of Cardioceras cor- 

 datum, in the lower Oxfordian. This might of course in this country 

 contain species of Aucella?, but in that case they ought to be forms of 

 that genus quite different from any found in Europe and representing 

 older and more primitive types, or else close allies of Aucella elongata or 

 other striated species of our zone of Cardioceras duhium. 



The faunas of mount Jura at Taylorville for the most part, as stated 

 above, are older than those in which Aucella? are found in Europe, and 

 so also is that described by Dr White from Alaska. Supposed Aucellse 

 have been found in the Upper Jura of western Europe, but, as stated by 

 Lahusen, they are not really species of this genus. 



In Russia, according to Pavlow "f aiid other authorities, notably Lahu- 

 sen, the zone in which Aucella makes its first appearance, that of Car- 

 dioceras alternans^ immediately succeeds in time the zone of Cardioceras 

 cordatuw,, now more properly designated Qiienstedioceras cordatam, both 

 being in the Oxfordian, the former unquestionably the younger. There 

 is therefore a sound basis for the conclusion that the Jura of the Gold 

 belt is younger than that of the Black hills and in part, at least, than 

 that of Alaska and the Aleutian islands. The direct evidence aff'orded 

 by the Ammonitinge of the rocks at Texas ranch, in Calaveras count}^ 

 where Cardioceras duhium represents Cardioceras alternans, places these 

 rocks as the equivalent of the upper Oxfordian in Russia. 



At the Stanislaus river locality there occurs Perisphinctes virgidatifonnis, 



* Bulletin no. 4, U. S. Geological Surve^^ 



fSyst. Jurass. de I'Est de la Russia : Bull. See. Geol. France, 3d ser., vol. xii, 1883-84, p. 086, 



