460 



MESOZOIC ERA— AGE OF REPTILES. 



Fig. 740, 



Fig. 742. 



Figs. 740-742. — California Jura-Trias Shells: 740. Grypheea spe- 

 ciosa (after Gabb). 741. Trigonia pandicosta (after Gabb). 742, 

 Ceratites Whitneyi (after Gabb). 



North Carolina and Virginia— i. e., Upper Triassic. Some of these 

 are given (Figs. 732-739). 



On the Pacific coast marine life no doubt abounded, as this was 

 the margin of an open sea; but the rocks here are very highly 



metamorphic, and 

 the fossils, there- 

 fore, mostly de- 

 stroyed. Wherever 

 this is not the case, 

 the rocks abound 

 in fossils. In Hum- 

 boldt County, Ne- 

 vada, for example, 

 the strata in some 

 places seem almost 

 wholly made up of 

 Ceratites Whitneyi 

 (Fig. 742). In the 

 same locality the remains of an Enaliosaur (sea-saurian) have been 

 found. On account of the marine conditions prevalent, the two peri- 

 ods are easily separable on the Pacific coast. 



Recent Discoveries. — Very recently in Colorado and Wyoming, in 

 beds which are referred to the Uppermost Jurassic, a large number of 

 most extraordinary reptiles have been found and described by Marsh 

 and Cope. Also, in the Wyoming beds, Marsh has discovered some 

 twenty-five species of Marsupial mammals and a reptilian bird (Lao- 

 pteryx). The beds from which all these have been taken are called, 

 from their most abundant and characteristic form, the 

 Atlantosaur beds. These discoveries are treated sepa- 

 rately, not only on account of their great importance, 

 but also and especially because they belong to an en- 

 tirely different horizon, viz., the uppermost Jurassic, 

 passing into the Cretaceous.* 



Dinosaurs. — The most abundant and the largest 

 reptiles found here are Dinosaurs. Some ten or twelve 

 species of this order have been described by Cope, and 

 fifteen or twenty species by Marsh. Some of these are Fig. 743.— Dorsal ver- 



J x J tebra of Ccelurus 



from the east slope of the Colorado Mountains, but fraguts, trans- 



, verse section (af- 



the most important have been found on the west slope. ter Marsh). 



* The Atlantosaur beds are classed with the Jurassic, because of the great gap between 

 it and the Dakota Cretaceous. But since this gap has been filled (see p. 473), the ques- 

 tion again returns whether they should be called Uppermost Jurassic or Lowermost Cre- 

 taceous. They apparently corresponds to the Wealden, which many geologists class with 

 the Cretaceous. Marsh, however, regards them as decidedly Jurassic. 



