PERMO-CARBONIFEROUS VERTEBRATES FROM NEW MEXICO. 3 



Other place, since it has been our experience in the Red Beds that detailed sections 

 made in any given place can not be depended upon perhaps a quarter of a mile 

 away. The top of this section, as already stated, yields vertebrate fossils of Upper 

 Triassic age, and some of the Triassic vertebrates described by Cope from New 

 Mexico came from El Cobre Canon. 



A survey of the surrounding country from the summit here, as also from the 

 Piedra Lmnbre, shows everywhere these basal Upper Triassic rocks as the lower 

 or lowermost exposures. 



From El Cobre Canon the expedition turned westward on the Chama to the 

 mouth of Caiiones Creek, and then southwest across the Piedra Lumbre Mesa to El 

 Rito ("branch") of the Puerco. The top of this mesa is formed of rocks of Upper 

 Triassic age, and near the base of Mount Pedemal, which rises several hundred feet 

 above the mesa, appears for the first time the heavy layer of gypsum marking the 

 upper limits of the Red Beds, or so-called Trias. From the top of this mesa a good 

 view of the adjacent country is afforded. To the north is the Mesa de los Viejos, 

 with the Chama apparently occupying a fault line between, and the Arroyo Seco in 



Fig. 2. — Map of region around Abiquiu, showing location of El Cobre Caflon. 



a valley formed by the basal Upper Trias rocks sloping from the brim of El Cobre 

 Canon on the east and the superincumbent Triassic rocks on the west. To the 

 west lie the Mesa Prieta and the smaller Capulin Mesa, separated by the Puerco, 

 Chama, and Capulin, streams whose courses seem to have been influenced strongly 

 by the faulting and dipping of the Trias. 



The Puerco, to the mouth of the Poleo, has cut down into Permian strata, which 

 attain their greatest exposure on the Poleo about a mile from its mouth. Our 

 first camp was made on the Poleo (Arroyo de Agua), about a mile above its con- 

 fluence with the Puerco.* Near the junction of the two creeks is a steep-walled 

 cliff of Permian rocks about loo feet in height, with a more or less fiat table-land 

 above it, a mile or so in extent, separating it from the Trias above. Farther west, 

 where the Permian rocks find their greatest exposure, and where the Baldwin 

 quarry lies, from which so many of the fossils in the Yale collection came, the very 

 steep bluffs, in many places so steep as to be unclimbable, are about 700 feet in 

 height. They are composed of alternating red sandstones and clays, with white 

 and purple sandstones, clays, and conglomerates at the upper part, corresponding 



• This Puerco Creek is not the one which gave origin to the name of the Puerco formation, 

 formatiun name was derived from a stream by the same name farther to the southwest. 



The 



