FORMATIONS OF THE NACIMIENTO GROUP 711 



formation described and named by Cross in 1892.^4 \i jg probable 

 that the Puerco of EndHch included some of the lower members of 

 the Wasatch which was determined in 1909 by J. W. Gidley and the 

 writer to lie next above the Animas formation in this portion of the 

 basin. The beds described by Holmes^ as Puerco in his Pinyon 

 Mesa section, about six miles north of the San Juan River and just 

 west of the La Plata River in New Mexico, may be either Puerco or 

 younger in age. He characterizes the formation as consisting of 

 "soft sand, clays, and marls, highly colored with reds, yellows, and 

 purples, growing gray below and containing masses of soft sandstone." 

 This description agrees more closely with the Canyon Largo series 

 of Newberry^ than with the Puerco. Holmes correlates Newberry's 

 Canyon Largo series with the Wasatch, which is probably correct, 

 since the beds occupy the innermost portion of the San Juan Basin and 

 could not well be older than Wasatch even though Newberry re- 

 ferred the whole series to the Cretaceous. 



Besides the collections of David Baldwin made during the years 

 1881 to 1888 no contributions were made to the Puerco fauna until 

 the year 1892. Baldwin died at his home in Farmington, New Mexico, 

 several years ago, and thus was lost to science a valuable collector 

 and with him much information never placed on record relative to 

 the geographic locations of many fossil-bearing districts. His original 

 collections which were described in numerous papers by Cope were 

 purchased in 1895 by the American Museum of Natural History in 

 New York City. 



In 1892 and 1896 the American Museum of Natural History sent 

 expeditions into the San Juan Basin for the purpose of further study 

 of problems connected with the Puerco fauna. This work was under 

 the direction of Dr. J. L. Wortman. As a result of these expeditions, 

 a large amount of new material was obtained. 



Some time after the first season's collecting by Wortman in 1892 

 a paper was written by Professor H. F. Osborn and Mr. Charles 

 Earle entitled "Fossil Mammals of the Puerco Beds."" In this 

 paper they quote the following field notes from Wortman: 



The thickness of the beds is roughly estimated at 800 to 1,000 feet, and as 

 far as can be observed they lie conformably upon the Laramie. At no place 

 examined by us can fossils be said to be abundant, but on the contrary most of 

 the exposures are entirely barren. For convenience they are divided into Upper 



