CAKBONIFEROUS UNDIVIDED. 357 



eruptive rocks constitute the Coxcomb Mountains, which have been crossed by 

 Cockburn, Fowler^ Wilson, and Sapper. Sapper's notes contain repeated references 

 to'phyllite clay slate and crinoidal limestones. Regarding the latter he says: 



Although the crinoidal limestones do not afford definite data for the determination of age, 

 since the crinoids are not specifically determinable, it is nevertheless most likely that the lime- 

 stone is Carboniferous, since it is only in this terrane thai; crinoidal limestones have thus far 

 been found in Guatemala. 



Crinoids are mentioned also as occurring in a gray~wacke. 



Since the position of these slates and associated limestones within the Carbonif- 

 erous is not definitely determined, the terrane is mapped as undivided Carboniferous, 

 but it is highly probable that the strata are of the same age as those of adjacent 

 areas in Guatemala, which, as stated in Chapter X (p. 425), are regarded by Girty 

 as not older than lower Pennsylvanian or uppermost Mississippian. 



H-I 12. SOUTHERN ARIZONA. 



Several isolated sections of Carboniferous strata in southern Arizona are 

 described by Ransome and Lindgren, and in the failure of exact equivalency they 

 are given local formation names: "Globe limestone" of the Globe district (upper 

 part only is Carboniferous), Escabrosa and Naco limestones of the Bisbee district, 

 and Modoc and Tule Spring limestones of the Clifton district. 



The "Globe limestone" consists almost exclusively of limestone in beds ranging 

 from 1 to 6 feet in thickness and attains a maximum of 700 feet. It rests without 

 angular unconformity upon the Apache group (Cambrian?), and is cut off at the 

 top by a plane of erosion. Ransome ''"'' states : 



It appears from the Piato Creek sections that the Globe formation includes in its lower 

 part at least 300 feet of Devonian strata and in its upper part at least 500 feet of Upper Car- 

 boniferous beds. No unconformity, however, has been found between the beds belonging to 

 these different periods. While future work in the broader region about the Globe quadrangle 

 may result ia the discovery of such an interruption of sedimentation and in the consequent 

 splitting up of the Globe limestone, it is believed that no such division is at present practicable 

 within the area covered by this report. ["] 



The case of the Globe limestone recalls that of the Ouray limestone in Colorado, to which 

 Cross has recently called attention. The Ouray limestone, an apparent stratigraphical unit 

 containing characteristic Devonian fossils, was at first referred wholly to that period. Later 

 work, however, has resulted in the discovery of Lower Carboniferous fossils in the upper part 

 of this limestone unit. There is nothing as yet known that precludes the presence of Lower 

 Carboniferous beds in the Globe limestone between the known fossiliferous Upper Carboniferous 

 and the known fossiliferous Devonian. The absence of any recognizable unconformity within 

 the mass of limestone strata is suggestive of uninterrupted deposition from the Devonian to 

 the Upper Carboniferous, and consequently of the presence of some Lower Carboniferous or 

 Mississippian. The paleontological note furnished by Dr. Girty also intimates that the Lower. 

 Carboniferous may be represented. 



The Escabrosa and Naco formations are Carboniferous limestones of the Bisbee 

 district, Arizona, the former having a thickness of 700 feet arid representing the 

 Mississippian series, the latter being 3,000 feet or more thick and equivalent to 

 the Pennsylvanian (Aubrey group and Redwall limestone of northern Arizona in 



o As a result of recent work in the Ray quadrangle, -wliich adjoins the Globe quadrangle, Ransome has separated 

 the Carboniferous from the Devonian. See Min. and Sci. Press, vol. 102, 1911, p. 747.— B. W. 



