FORMATIONS OF THE NACIMIENTO GROUP 713 



HISTORY OF THE TORREJON 



The possibility of distinction between the faunas of the upper and 

 lower beds of the original Puerco had been noted by Cope. In his 

 paper on the " Synopsis of the Vertebrate Fauna of the Puerco Series"^^ 

 inji888 he stated that the information at that time available indicated 

 some faunal difference between the lower and upper beds. In bearing 

 out this view he gave a list of twenty species pecuHar to the lower 

 beds, leaving to research to determine whether or not they occur also 

 inj the. upper beds. 



Afterj the field expeditions of the American Museum of Natural 

 History in 1892 and 1896, a systematic revision of the fauna from 

 Cope's Puerco was taken up by Dr. W. D. Matthew, of that organi- 

 zation. In his paper of 1897 entitled "A Revision of the Puerco 

 Fauna "44 he emphasized the absolute distinctness in the faunas of the 

 upper and lower beds, stating that they contain not a single species 

 in common and that not a genus passes through without serious modi- 

 fications of at least subgeneric value. The faunas were found to be 

 as different as any other two successive Eocene formations, and it 

 became necessary to adopt a new name to designate one of the two. 

 It was then that Dr. Wortman proposed the name Torrejon formation 

 for the upper beds, retaining the name Puerco for the lower. The 

 name Torrejon was taken from the arroyo of that name in the type- 

 locality. It has since been freely used and is firmly fixed in literature. 



In 1 901 Mr. Earl Douglass discovered Torrejon fossil vertebrates 

 in Montana, ^^ a fuller reference to which will be given under the 

 head of "Correlations." With the exception of the one locahty in 

 Montana, no fossils have been found elsewhere in the United States 

 corresponding to either of these unique faunas of the Nacimiento 

 group of the San Juan Basin in New Mexico. 



NAMING OF THE NACIMIENTO 



In view of the fact that the Puerco was restricted to the lower 

 formation when the name Torrejon was proposed, and since it is 

 very necessary to adopt a group name in order to properly discuss 

 the relationship of the two formations, the writer proposes the name 

 Nacimiento group for the two formations used collectively. The rela- 



