814 



SCIENCE. 



[N. S. Vol. IV. No. 101. 



The next noteworthy description of the 

 Jurassic as here defined was given by J. C. 

 Booth in his report on the Geological Sur- 

 vey of Delaware, 1841. He described the 

 variegated plastic clays of that state, and 

 gave to them the name of ' Eed Clay For- 

 mation,' which he regarded as belonging to 

 the Upper Secondary. The more recent pub- 

 lications on this Atlantic Coast formation 

 are well known, and need not be cited here. 



Among the early explorers who contri- 

 buted to our knowledge of the Jurassic of 

 the E.ocky Mountains and Pacific coast 

 region were J. Marcou, in New Mexico, 

 1853 ; C. King, in California, 1863 ; and, in 

 the same State, W. Gabb, 1864, and F. B. 

 Meek, 1865. 



The earliest discovery of the Jurassic in 

 the Arctic region of this country was by 

 Sir E. Belcher, in 1852, who found remains 

 of Ichthyosaurus on Exmouth Island. The 

 latest information in regard to the Jurassic 

 comes also from the Arctic region, where 

 Nansen has found this formation contain- 

 ing many fossils, near Franz Josef Land. 



JUKA-TRIAS. 



The term Jura-Trias, now in use, is in 

 reality a confession of ignorance, excusable, 

 perhaps, a quarter of a century ago, but un- 

 pardonable now in those whose duty it is to 

 map or define the formations of this coun- 

 try. Yet this term is still sometimes used 

 for so clean-cut a Triassic horizon as the 

 Connecticut River sandstone. It is true 

 that in early days of New England geology 

 this formation was in part referred to the 

 Jurassic, but at the present time no one at 

 all familiar with the evidence of the abun- 

 dant vertebrate life found in it could make 

 such a mistake. This is equally true of the 

 southern extension of the same formation 

 along the Atlantic coast, where it is every- 

 where quite distinct from the Jurassic. In 

 the West the dividing line is less marked 

 in some regions, but I believe that even 



there careful explorations alone are required 

 to separate these two allied formations. 



VERTEBRATE FAUNA OF THE JURASSIC. 



The Jurassic age of the Atlantosaurus 

 beds of the West has now been demon- 

 strated beyond question by the presence of 

 a rich fauna of mammals, birds, reptiles, 

 and fishes. Among these the Sauropoda 

 were dominant and the other Dinosaurs 

 well represented. 



In the Potomac beds of Maryland the 

 same Jurassic vertebrate fauna is present, 

 as shown by the remains of five different 

 orders of reptiles already discovered in 

 them. Among the Dinosaurs are the Sau- 

 ropoda, the Theropoda and the Predentata, the 

 first group represented by several genera 

 and a great number of individuals. One 

 of these genera is Pleuroccelus, which has 

 also been found in the Jurassic of the West. 

 Besides the Dinosaurs, characteristic re- 

 mains of Crocodilia and Testudinata are not 

 uncommon, and various fishes have been 

 found. The remains of these six groups 

 already known are amply sufficient to de- 

 termine the age of the formation, and still 

 more important discoveries doubtless await 

 careful exploration. 



The discovery of vertebrate fossils further 

 east is merely a question of systematic 

 work. That they are there, all experience 

 in this horizon clearly indicates. In 1870 

 I passed over miles of similar strata on the 

 eastern flanks of the Uinta Mountains, with 

 every man of my expedition on the lookout 

 for fossils, prompted both by zeal for science 

 and a special reward for the first specimen, 

 but also on the alert for the hostile Ute 

 Indians around us, yet not a fossil was 

 seen. Ascending a few hundred feet, I 

 found the sides of a narrow canyon full of 

 fossils, vertebrate and invertebrate, all of 

 Jurassic forms. The stratum once estab- 

 lished, the supposed barren clays soon fur- 

 nished rich localities. 



