42 RAYMOND C. MOORE AND FREDERICK B. PLUMMER 



Clearer waters, in which calcareous muds and limestones were 

 the chief accumulating sediments, succeeded, the Canyon group 

 representing the second epoch of dominant limestone formation in 

 the Texas Pennsylvanian. Some 700 or 800 feet of limestones and 

 shales were deposited during this relatively quiet interval, the 

 invertebrate faunas showing only changes which might be antici- 

 pated with undisturbed, clear waters. It is probable that the 

 change to dominant limestone deposition in Texas was approxi- 

 mately synchronous with the similar change in the northern part of 

 the mid-continent region above the Cherokee shale. 



The beginning of Cisco time is marked by a change in the 

 character of the sediments, a great amount of mud, sand, and 

 gravel being swept from the north and northeast, where the orogenic 

 movement which resulted in the formation of the Arbuckle Moun- 

 tains and probably an uplift of the ancient land of Llanoria fur- 

 nished an abundance of materials. The thick, relatively soft, 

 clastic formations which compose the Lower Pennsylvanian in the 

 Arbuckle region would first be exposed to erosion and probably 

 furnished a large proportion of the sediment in the Graham forma- 

 tion of north Texas. When the Lower Paleozoic limestones of the 

 mountain areas were exposed, limestone conglomerates were formed 

 locally (Franks) which were strewn across the eroded edges of the 

 earlier Pennsylvanian. Although there is an important uncon- 

 formity in this part of the Pennsylvanian of southern Oklahoma, 

 the seas do not appear to have receded more than temporarily from 

 north Texas, for the unconformity at the top of the Graham forma- 

 tion is not a large one. However, the faunas underwent a striking 

 change and throughout the remainder of the Cisco have a very 

 evident late Pennsylvanian aspect. The middle and upper Cisco 

 represents a continuation of mud and sand deposition with an 

 occasional limestone bed and one or two important intervals when 

 coal was formed. There does not appear to have been any marked 

 change with the transition to Permian time in part of the north 

 Texas region, but to the northwest the presence of continental 

 Red Beds sediments characteristic of the Permian appears. In 

 these are found the well-known reptiles and amphibians which lived 

 on the early Permian lands and along the old shores in the north 

 Texas region. 



