Marsh — Jurassio formation on the Atlantic Coast. 445 



Vertebrate Fauna of the Jurassic. 



The Jurassic a^e of the Atlantosaurus beds of the West has 

 now been demonstrated 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 verte- 

 brate fauna is present, as shown by the remains of five differ- 

 ent orders of reptiles already discovered in them. Among 

 the Dinosaurs are the Sauropoda^ the Theropoda^ and the 

 JPredentata, the first group represented by several genera and 

 a great number of individuals. One of these genera is 

 Pleurocmlus, which has also been found in the Jurassic of 

 the West. Besides the Dinosaurs, characteristic remains of 

 CroGodilia and Testudinata are not uncommon, and various 

 Fishes have been found. The remains of these six groups 

 already known are amply sufiicient to determine the age 

 of the formation, and still more important discoveries doubt- 

 less await careful exploration. 



The discovery of vertebrate fossils further east is merely a 

 question of systematic work. That they are there, ail experi- 

 ence 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 established, the supposed 

 barren clays soon furnished rich localities. 



The similar Potomac clays were formerly pronounced quite 

 destitute of animal remains by geologists of eminence, but hard 

 work disclosed their treasures. The coast east of the Hudson has 

 an abundance of the same strata, and offers still greater rewards 

 to explorers. The G-ay Head Indians are not hostile, but will 

 be found active assistants in the good work, while holding fast 

 to the traditions of their ancestors as to the volcanic origin of 

 their narrow sea-scourged home. 



Long Island Sound. 



It is evident that we know the remnants only of the great 

 formation we are now discussing, for the larger part of it has 

 long since been swept away, and much of the remainder is 

 covered up or obscured by later deposits. The origin of 

 this formation is a great question in itself, while its gradual 

 destruction offers still larger problems to the geologist. One 

 of these only I have time now to touch upon, and that has 

 special interest for me, as day by day from my study window 

 I look across the Sound to Long Island. 



