characteristics of upper carlile member 497 



The Upper Carlile Member 



In writing of this Upper Carlile member, Darton^ says: 



"At the top there is a bed of sandstone varying in thickness from a few 

 inches to 20 feet, the amount increasing to the west. . . . The top sand- 

 stone averages 10 to 20 feet in thickness west of longitude 104 and attains a 

 maximum of 30 feet at Greenwood, on Hardscrabble Creek, and near Chandler, 

 south of Canyon. Near La Junta it is three feet thick. . . . Usually it is 

 soft, somewhat mixed with sandy shale, and of yellowish color. The fossil 

 known as Pugnellus occurs abundantly in the formation in the southwestern 

 portion of the area." 



Writing of this same Upper Carlile member as it occurs in the Apishapa 

 Quadrangle some 30 miles west of La Junta, Stose^ describes it as fol- 

 lows: 



"In most places yellow sandstone 10 to 20 feet thick occurs at the top. The 

 sandstone is calcareous in fresh exposure and is generally very fossiliferous 

 in the upper part, its fragments being marked by casts of a large, strongly 

 ribbed coiled ammonite, Prionocyclus wyomingensis.'' 



This upper sandstone member thins out on approaching La Junta and 

 becomes three feet thick or less. At the same time it loses its sandy 

 character and becomes a crystalline limestone of grayish color that 

 weathers to a dark rusty brown. It is also very fossiliferous, containing 

 the same fossils mentioned above by Darton and Stose and including 

 abundant Ostrea and occasionally sharks' teeth. Stose mentions the fact 

 that the sandstone in the Apishapa Quadrangle in fresh exposure is 

 calcareous. In the La Junta area it becomes altogether a limestone that 

 is invariably crystalline. A typical sample of this rock dissolved in 

 hydrochloric acid gave less than 1 per cent insoluble matter. 



This upper limestone member is, in most of the La Junta area, sharply 

 defined from the overlying Timpas limestone ; but northeast of La Junta 

 a change is to be noted. The rock loses in part its crystalline appearance 

 and its uniform brownish color and becomes mottled white and broMai. 

 The irregular brown spots appear almost like inclosed fragments in the 

 prevailing grayish white mass; but the frayed nature of the boundary 

 line of these brown spots shows that they are due to local oxidation of 

 the furruginous contents or to infiltration. At the same time the stratum 

 loses its sharply defined upper edge and it becomes impossible to draw 

 the line between this supposed Carlile member and the overlying white, 

 chalky Timpas limestone. The two are apparently one. 



2 N. H. Darton : TJ. S. Geol. Survey, Professional Paper No. 52, 1906, p. 28. 



3 George W. Stose : Folio, U. S. Geol. Survey No. 186, 1912, p. 6. 



XXXIII — Bill. Geol. See. A.m., Vol. .34, 1922 



