410 A. HYATT GEOLOGY OF THE TAYLORVILLE REGION. 



Jura of Europe. A fine scries of ammonitinse collected at Aurora, Wyo- 

 ming, shows the presence of the same species as those occurring at the 

 Black hills, and other fossils arc also identical. The genera to which they 

 belong arc all included in the group of the cardioceratidse, under which 

 name I unite the genera Cardioecras, Cadoceras, Quenstedioceras and Neu- 

 mayria, all of them being peculiar to the Callovian and Oxfordian in 

 western Europe and Russia. Although very often confounded with the 

 amaltheidse of the Lias, these genera have entirely different young forms 

 and adult characteristics, especially in the sutures, and also have sprung 

 from different ancestral radicals. 



On going a step farther, however, and comparing the species* with 

 those of the supposed Callovian of mount Jura it becomes evident that 

 they have no species common to both ; but, on the other hand, Camplo- 

 nectes bellistriatus and possibly some other pelecypods and brachiopods 

 are found occurring not in the supposed Callovian, but in the supposed 

 Corallian of Plumas county. This unexpected result is in accord with 

 the very distinct faunas of the Bicknell sandstone, or Trigonia bed, and 

 of the Hinchman tuff, which do not permit us to suppose any very open 

 or direct connection existed with the upper Jurassic faunas of the Rocky 

 mountain region, and is in accord with the similar facts observable in 

 the Oolite. 



When attempts are made to compare the Oolite of the Rocky mountain 

 region with that west of the Sierras, existing information with regard 

 to the localities is found to be very imperfect. The Oolite certainly seems 

 to have been found by Dr. Peale near the lower canyon of the Yellow- 

 stone in Montana, and out of the few fossils described by Dr. White some 

 are closely similar to these of the inferior Oolite at mount Jura. Modiola 

 subimbricata is apparently common to both faunas, and some of the species 

 of Gervillia may la' identical ; but the species of Trigonia are entirely dis- 

 tinct from those of mount Jura. 



Oasteropods and cephalopods have not been noticed in these Oolitic 

 faunas. While this may be owing to insufficient collecting, it is well 

 to note the fact; for although the remains of Oolitic ammonites have 

 been occasionally picked up west of the crests of the Sierra Nevada, 

 no such finds have thus far occurred cast of that line, so far as known 

 to me. 



The lower Lias, containing characteristic ammonitinse, one species of 

 which (Amioceras humboldti) was described in my "Genesis of the Arie- 

 tidse," occurs in the region formerly called the American district, Nevada. 



*The entire absence of gasteropoda from these deposits has been noted by Whitfield in his report 

 on the fossils of the Black hills, and the same may be* said with regard to the marine faunas at 

 Aurora, Wyoming, and other localities mentioned above. 



