CARBONIFEROUS UNDIVIDED. 361 



I 12. ARIZONA AND NOKTHWlS STERN NEW MEXICO. 



Reagan ^®^* states in regard to the Carboniferous of the Fort Apache region, 

 in Arizona: 



Lower Redwall group. — -The first series above the Devonian is from 400 to 1,000 feet of 

 alternating gray limestone and shale. It terminates at the top in a massive to shaly coarse 

 sandrock, often of the millstone grit tjrpe. The lime rocks are very f ossUif erous from the middle 

 of the series to the top and seem to belong to the lower Carboniferous group; but as yet the 

 writer has not identified fossils enough from the group to verify such a conclusion. 



Upper Redwall group. — -The writer has included in this group all of the strata superim- 

 posed on the millstone grit rock of the group just described, to and including the dark-gray 

 limestone series about 1,000 feet above its base. The series here is very variable, indicating 

 a rapid transformation from west to east. Ripple marks and old shore lines are noticeable 

 and indications of large swamp land areas are exposed on Cibicu Creek and in the vicinity of 

 Fort Apache. As evidence that the country reached the swamp stage the writer found several 

 specimens of Lepidodendron and one whole tree of the species Calamites cannseformis. The group 

 belongs to the coal-measure series, as is attested by its fossils: Spirifer cameratus, Productus 

 semireticulatus , P. costatus, Lepidodendron, Calamites cannseformis, etc. 



Aubrey group. — The interstream spaces of aU the streams in their upper course, as well 

 as the south front of the Mogollon Range and the Cibicu divide, where not covered with later 

 deposits, are capped with 280 feet of calcareous sandstone followed by 500 feet of soft red and 

 gray shales, interrupted by sectUe limestone. The Aubrey limestone occurs in one locality — ■ 

 at the headwaters of the Cibicu and Canyon creeks. The rocks of this group are usually non- 

 fossUiferous, but fossils enough were obtained {Athyris suhtilita, Productus punctatus, Spirifer 

 cameratus, Productus, and Bellerophon) to identify it as upper Carboniferous. 



The Zuni Plateau lies just north of the thirty-fifth parallel in New Mexico. 

 It is composed largely of Carboniferous strata, which Button ^"'' discusses and 

 compares as follows: 



The Carboniferous strata of the plateau country have been divided into two portions, an 

 upper and lower. To the lower portion the local name of the "Redwall group" has been given 

 and the upper portion has been named the "Aubrey group." The Redwall takes its name from 

 the great vertical escarpments which its most massive member presents in the canyons of the 

 Colorado. In the Grand and Marble canyons especially a band of limestone from 800 to 900 

 feet thick constitutes the face of the principal vertical cliff and becomes the most impressive 

 stratigraphic feature of those great chasms. It has always been spoken of as the Red Wall. 

 Its lower Carboniferous age has been well ascertained. Above and below it are numerous 

 bands of limestone and calcareous sandstones belonging to the same group and always classed 

 with it. While it is always found at the exposures of its proper horizon in the other parts 

 of the plateau country, it is plainly wanting in the district we are about to study, and its 

 absence is certainly a striking fact. It appears to be absent also from the Nacimiento Range, 

 northeast of the Zuni Plateau, where the upper Carboniferous rests on the Archean just as it 

 does here. In southern and southwestern Colorado, however, it is usually found in its proper 

 place. The conclusion seems obvious that it was never deposited here, and that this locahty 

 was a land area in early Carboniferous time. 



The upper Carboniferous or Aubrey group is usually subdivided into two portions, an 

 upper and a lower Aubrey. This subdivision is quite proper as well as convenient, for the 

 two portions are strongly contrasted with each other in their lithologic features and in the 

 topography to which their erosion has given origin. The lower Aubrey consists of bright-red 

 sandstones throughout, deposited usually in rather thick and less frequently in moderately 

 thin layers. They are much alike in aU outward respects, color, texture, and grouping and in 

 the erosional forms sculptured out of them. They are very. fine grained, without traces of 

 conglomerate or coarse shingle or gravels, and, having a calcareous cement, they weather easily 



