ARTICLE V. 



SYNOPSIS OF THE VERTEBRATE FAUNA OF THE PUERCO SERIES. 



BY E. D. COPE. 



Read before the American Philosophical Society, January 20, 1888. 



The Puei-co formation rests on the Laramie in IS'orthwestern New Mexico and 

 Sonthwestern Colorado, and is largely covered by the Wasatch Eocene in both 

 regions. It was discovered by the writer in 1874 at its eastern outcrop of about 500 

 feet thickness, and was identified by Endlich and Holmes in Colorado in 1876, where 

 the thickness reaches 1000 to 1200 feet. On the San Juan river its thickness is 700 

 feet, while at its western outcrop south of that river, its thickness is 800 or 900 feet. 

 "While the 'formation possesses lithological peculiai-ities, no clue to its importance in 

 geologic chronology was known until the discovery of vertebrate remains was made 

 in 1880, by Mr. David Baldwin. With the evidence derived from this material, the 

 writer has been able to interject into the series of epochs of geological time a period 

 which must have possessed many peculiarities, and which differed in such important 

 essentials from those which preceded and from those that followed it, that an immense 

 interval between them is proven to have existed, such as had not been previously sus- 

 pected. The rich fauna which it contains displays characters which indicate other 

 discoveries yet to be made befoi'c connections with other epochs both prior and subse- 

 quent can be known. 



The vertebrate fauna includes up to the present date one hundred and six known 

 species. Four species of Mollusca have been discovered, which have been determined 

 by Dr. C. A. White of the U. S. National Museum. They are Unio rectoides White ; 

 Helix adijns White ; H. nacimientensis White, and Pupa leidyi Meek, The first 

 named is found in the Wasatch, and the last in the ? Bridger ; the two other species 

 are peculiai*. Besides these the only other indication of organic life at that period is 

 petrified wood of undetermined trees, which is quite abundant. 



