620 L. C. SNIDER 



Muskogee quadrangles this unconformity is not very striking as is 

 shown by the mapping of the Chester Hmestone in the Tahlequah 

 with the underlying Boone and by its separation from the Boone 

 in the Muskogee only on account of the fauna and the thin layer 

 of shale at the base of the limestone. In the Pryor quadrangle, 

 however, this unconformity is very pronounced and the hills of 

 typical Boone chert protrude through the limestone in several 

 places, and in at least one place (hill just east of the town of Pryor 

 Creek) through a considerable portion of the Fayetteville shale. 

 The tops of some of the hills of Boone chert are at approximately 

 the same level as the tops of other hills in the vicinity which are 

 capped by the Pitkin limestone. The conditions are represented 



P/fkin Limestone. 



^^^^^^^^^ Fayetteville Shale . 



r~~r~T^-T- 



C3 <=> \<=S^J^ 



xzT^ Limestone. 



]j=:\^ ^c^ \^ \^ \^\^ -^^\ <=^\^\ -^\c^\<=>\ Boone Chert. 



Fig. 2. — Diagram illustrating unconformity at top of Boone formation in the 

 Pryor quadrangle. 



diagrammatically in Fig. 2. When these hills were first observed 

 they were thought to be structural domes but more careful work has 

 shown that the limestones and Fayetteville shale lie up against 

 the chert in a horizontal position so that the presence of a pro- 

 nounced unconformity seems to be the only hypothesis which 

 accounts for the hills of chert above the level of the unnamed 

 limestone and the Fayetteville. 



Fayetteville shale. — Near the Arkansas line in the Tahlequah 

 quadrangle the Fayetteville shale is reported as reaching a thick- 

 ness of 120 feet, but in the Muskogee quadrangle it is said by Taff 

 not to exceed 60 feet. In a section measured southeast of Ft. 

 Gibson by Ohern and the writer, however, the Fayetteville shows a 

 thickness of about 100 feet. The formation consists principally 

 of blue to black, fissile clay shales with thin limestones, usually 

 lenticular. In the Tahlequah quadrangle there is a sandstone 



