faung 



C. A. Heeds — Hunton Forynation of Oklahoma. 257 



horizons : Clinton, Niagara, Helderberg and Lower Oriskany, 

 the first and second assigned to the basal member, the third 

 and fourth to the middle and upper members, respectively. 



The writer does not accept this threefold lithologic and four- 

 fold paleontologic subdivision of the Hunton. Instead, he pro- 

 poses both a fourfold lithologic and paleontologic arrangement, 

 the new units to have the rank of formations. From bottom 

 to top they are (1) the Chimneyhill limestone (Silurian), (2) 

 the Henryhouse shale (Silurian), (3) the Haragan shale (Devo- 

 nian) and (4) the JBois d'Arc limestone (Devonian). These 

 four formation names are new terms and have been approved 

 by the Committee on Geologic Names of the U. S. Geological 

 Survey. As may be seen from the correlation table, Table 1, 

 the limits of the new subdivisions do not correspond exactly 

 with those proposed by Taff, Ulrich and Girty. 



This difference in the grouping of the beds has arisen, no 

 doubt, from the unrealized very variable thickness of the 

 Chimneyhill, Henryhouse, Haragan and Bois d'Arc formations 

 from place to place, and also because the characteristic fossils 

 which definitely define the limits of each had not then been 

 determined. In Taff 's type area at Hunton only three of the new 

 formations here proposed, the Chimneyhill, Haragan and Bois 

 d'Arc, are present, the Henryhouse having been eroded previ- 

 ous to the deposition of the Haragan. In the Lawrence anti- 

 cline, however, some 15 to 20 miles northwest from Hunton 

 the Henryhouse formation attains its greatest thickness, 223 

 feet, while the Haragan formation is wanting. There the Bois 

 d'Arc rests disconformably on the Henryhouse while the latter 

 is disposed similarly on top of the Chimneyhill. In the " White 

 Mound " region 3 to 4 miles southeast of Dougherty, and many 

 places elsewhere, the four formations are present, but vary- 

 ing in thickness from locality to locality. No two of the 35 

 sections made across the Hunton are alike. Not only are the 

 entire sections of different thickness but also the amount of 

 each formation present is variable. The cause for this varia- 

 bility is assigned to unequal rate and time of deposition from 

 place to place, and also to differential erosion during and follow- 

 ing sedimentation. 



The writer's classification is based on both faunal and litho- 

 logic grounds but primarily on the faunal evidence. In locali- 

 ties where the Haragan shale rests on the Henryhouse shale, as 

 in the exposures about Dougherty, it will be difficult, without a 

 knowledge of the fossils, to separate one formation from the 

 other. In localities where only one of these shale members is 

 present, as near Lawrence and Hunton, there will be no diffi- 

 culty in distinguishing three formations, lithologically as well as 

 faunally. The fossils, however, are the only criteria that may 



