RESUME — ORDOVICIAN, DEVONIAN, CARBONIFEROUS 435 



carry a Richmond fauna of upper Ordovician age. The upper limits 

 are somewhat indefinite, but doubtless there is a great planation uncon- 

 formity and hiatus separating the Lower Carboniferous limestone. In 

 the Black hills the Ordovician, which has been designated the White- 

 wood limestone, appears in the northern portion of the uplift and to 

 a limited extent in the Bear Lodge range. It carries an upper Trenton 

 fauna, and from this fact and the close lithologic similarity, it is believed 

 to be equivalent to the lower massive member of the Bighorn limestone. 

 The few feet of green shales which lie above the Whitewood limestone 

 are of undetermined age. No evidence of Ordovician rocks were de- 

 tected in the Casper or Laramie ranges, the Hartville uplift, or in the 

 Rocky Mountain front ranges north of Denver. It is possible that they 

 were deposited and removed by pre-Pennsylvanian erosion. The Ordo- 

 vician rocks which appear in the central portion of the Front range in 

 Colorado — the Manitou limestone, Harding sandstone, and Fremont 

 limestone — contain a Trenton fauna, the Harding sandstone represent- 

 ing the lower Trenton and the Fremont limestone the upper Trenton. 



SIL URIA N-DE VON I A N 



No deposits representing these two great periods of geologic time have 

 been discovered in the area to which this report relates. They are surely 

 absent in the Front range exposures in Colorado, but may possibly be 

 represented in the green shale of the northern Black hills and in the 

 zone of apparently non-fossiliferous limestones lying between the Big- 

 horn and Littlehorn limestones of the Bighorn uplift. I think, how- 

 ever, it is much more likely that they are entire]} 7, absent along the east 

 side of the Rocky Mountain uplift, although they may underlie a por- 

 tion of the Great plains eastward. 



LOWER CARBONIFEROUS 



The Lower Carboniferous rocks are exposed principally in the Black 

 hills and Bighorn uplifts, and a few small areas occur along the foot of 

 the Front range, in Colorado. It is probable that these rocks extend 

 widely under the Great plains, but no borings have gone deep enough 

 to reach them, except in eastern Kansas and southeastern Nebraska. 



In the Black hills the Mississippian is represented by two limestone 

 formations, the Englewood and the Pahasapa, both containing an abun- 

 dance of characteristic fossils, those of the Englewood being equivalent 

 to the lowest Mississippian (Chouteau or Kinderhook) and the Pahasapa 

 equivalent to the Madison limestone of the northwest. Some Leperditia 

 in the concretions in red shale at the base of the Minnelusa are of a type 



