BULLETIN OF THE GEOLOGICAL SOCIETY OF AMERICA 



Vol. 34, pp. 495-498 SEPTEMBER 30, 1923 



MERGING OF CAELILE SHALE AND TIMPAS LIMESTONE 

 FORMATIONS IN SOUTHEASTERN COLORADO^ 



BY HORACE BUSHNELL PATTOX 



{Presented before the Society December 29, 1922) 



CONTENTS 



Page 



Introductorj^ 495 



The Upper Carlile member 497 



■Carlile fossil in the Timpas limestone 498 



INTRODUCTORY 



In connection with field-work undertaken for the Colorado Geological 

 Survey the past summer in the vicinity of La Junta, Colorado, the author 

 has had occasion to note a gradual transition or merging of two forma- 

 tions that heretofore have been considered as belonging to two different 

 groups, the Benton and the Niobrara grou23s. The present communica- 

 tion is presented with the consent of the Director of the Survey. 



In southeastern Colorado the Benton group is developed as three 

 readily distinguished formations. The lowest of the three is the Graneros 

 shale, with some 200 feet of gray to black shales. The highest, or Carlile 

 shale, has usually about the same thickness and is likewise composed of 

 dark gray shales, which at the top change to a yellowish sandstone of 20 

 feet thickness or over. The two are separated by some 50 feet of Green- 

 horn limestone. The Niobrara group lias a twofold division — into the 

 Timpas limestone at the bottom and the Apishapa shale at the top. The 

 two together have a thickness of some 700 feet, of which 500 feet belong- 

 to the Apishapa and 200 feet to the Timpas. The upper 150 feet of the 

 Timpas are composed of gray shales with occasional thin beds of white 

 limestone. The lower 50 feet consist of massive beds of soft, almost 

 chalklike limestone, one to two feet thick, separated by very thin shale 

 partings. The contact between the basal limestone of the Timpas and 

 the underMng top sandstone of the Carlile shale is usually very sharp. 



1 Manuscript received by tlie Secretary of tlie Society December 30, 1922. 



(495) 



