118 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 127 
a feather edge to 100 feet in thickness. It is mostly dense blue-gray limestone 
often resembling lithographic limestone. The few brachiopods listed are: 
Ancistrorhyncha costata Ulrich and Cooper Strophomena cf. incurvata (Shepard) 
Camerella aff. C. panderi Billings Zygospira aff. Z. recurvirostris (Hall) 
Rafinesquina aff. R. alternata (Emmons) 
This is a short list, but the presence of Rafinesquina aff. R. alternata suggests 
that part of this formation should be correlated with the Decorah-Barnhart rather 
than all with the Plattin. It may be noted that in the Missouri occurrences of 
Plattin true Rafinesquina is unknown, but this genus is abundant in the over- 
lying Barnhart. In the Batesville region Ancistrorhyncha is common and is a 
good indicator of the lower Plattin. 
8. THE ARBUCKLE AND WICHITA MOUNTAINS, OKLAHOMA 
The rocks of the Arbuckle and Wichita Mountain areas include an important 
section of early Middle Ordovician strata known as the Simpson group. This 
group consists of five formations, all of them originally proposed in charts or 
correlation tables. The history of the nomenclature of the Simpson group is 
discussed fully by Loeblich (1942, pp. 413-416) and need not be repeated here. 
Detailed description of the formations was published by Decker and Merritt 
(1931) and later elaborated by Decker (1941). As is usual with many for- 
mations in the United States, stratigraphic information may be had in minute 
detail, but the paleontology has never been well done. So it is with the Simpson 
group. The only paleontology besides Loeblich’s (1942) description of the 
Bryozoa of the upper Simpson is the faunal listing attempted by Decker (in 
Decker and Merritt) in 1931. These lists are most unsatisfactory because they 
contain numerous identifications of genera and species now known not to occur 
anywhere in the Simpson sequence. In at least one instance Richmond species 
have been identified in a formation that cannot be younger than the Porterfield 
stage. 
At present, and on the basis of Decker’s work (1941), five formations are 
recognized in the Simpson group. Ulrich (1933) distinguished eight formations, 
but three of them were not accepted by Decker. It seems best to follow Decker 
in this matter at the present time, but it is possible that the future may see 
further splitting within the group. The five formations recognized are, from the 
base up: Joins, Oil Creek, McLish, Tulip Creek, and Bromide. Herein the 
Bromide is divided into two members. Faunal affinities of the formations are 
with the Appalachians and with the Great Basin. Like their geographic situa- 
tion between the Appalachian and Great Basin areas, the faunas also indicate. 
intermediate relationships to both realms. 
Joins formation.—This formation consists of thin limestones and shales vary- 
ing from 30 to 296 feet in thickness. It is limited to the middle southern and 
western parts of the Arbuckles and the north end of the Criner Hills. The forma- 
tion abounds in the brachiopod Desmorthis nevadensis, which was formerly re- 
ferred to Orthis costalis Hall by earlier workers. Desmorthis costata Cooper is 
