CONCLUSION. 



In Europe, where the succession of the Mesozoie roclvs has been traced 

 out in more minute detail than in North America, and where the animal 

 life of the age is better known, it is found that its marine fauna is con- 

 tinuous throughout, with only local exceptions. The Ehastic beds hold 

 fossils which pass from the Trias into the Lias, and M. Ernest Favre has 

 shown that the Jurassic and Cretaceous strata of the Alps are not 

 sej)arated, as in the Anglo-Parisian basin, by fresh water deposits. In 

 1865, Prof Oi^pel, of Munich, proposed the name of the Tithonic Group 

 for certain rocks which occur in Spain, Italy, Switzerland, Austria, &c., 

 and which were then believed (o be the equivalents of the Portland Oolite 

 and Purbeck beds of England. Still later, Dr. JSTeumayr has suggested 

 the division of this group into an Upper and a Lower .series. It is by 

 no means certain that the Upper Tithonic strata are exactly synchro- 

 nous with the English Purbccks, but it is tolerably clear that the former 

 represent the cxti'cme top of the Jurassic Series as undcj'stood by 

 European geologists. The Up})ei' Tithonic de])(isits are beds of passage 

 between the Jurassic and Cretaceous, and contain a small j^ercentage of 

 marine fossils wliich pass upwards into the Lower Neocomian. Aucella 

 Entnyt'jni, from the auriferous and presumablj' Jurassic slates of the 

 Sierra Nevada, may be identical with the ^-1. PiochU of the Shasta 

 Group of California, but, with this exception, ]io fossil is known to be 

 common to the Jurassic and Cretaceous formations in America. 



A' diflerent classification of the Cretaceous rocks is adoj'jfed in two of 

 the most popular and recent hand-books of geology. Professors Jukes 

 and Geikic''^ recognize only an Uj)2)er ai^d a Lower Cretaceous group, 

 and place the Wealdon at the base of the latter. In the second edition 

 of Prof. Dana's "Manual of Geology," dated 1874, the period is divided 

 into Upper, Middle and Lower Cretaceous, while the Wealden is 

 regarded as a separate epoch, belonging to the upper part of the 

 Jurassic. As Prof. Dana's manual is universally used in America, it 

 will be more convenient to adopt his arrangement. 



* "The student's Manual of Geology." By J. Beetc .Jukes, MA., F.E.S. Third Edition, Edited by 

 Archibald Geikie, F.K.S. Edinburgh : as72. 



