228 INDEX TO THE STRATIGRAPHY , OF NORTH AMERICA. 



H 13. TBANS-PECOS TEXAS. 



With reference to the Silurian in the district lying north and east of El Paso 

 Richardson ^^^^ states: 



The Silurian system in trans-Pecos Texas is represented in the El Paso region [by] the 

 Fusselman limestone in the Franklin and Hueco mountains. This is a naassive whitish magne- 

 sian limestone approximately 1,000 feet thick. It OTerlies the Montoya limestone apparently 

 conformably, although in one locality fragments of the underlying limestone included in the 

 Fusselman give evidence of an unconformity. Throughout the greater part of the formation 

 fossils are scarce, but at a few horizons they are very abundant. The commonest form is a 

 species of radially plicated pentameroid shell which, with Amplexus and Favosites, determined 

 by Mr. Ulrich, proves that the upper Niagaran stage of the Silurian is here represented. Gordon 

 and Graton " have recently found Silurian fossils in the Silver City region and at Lake Valley, 

 N. Mex. ; and Taff 's Hunton formation in Oklahoma ^ also contains a Silurian fauna. 



I 12. ARIZONA. 



Reagan ^^^ states in regard to the Silurian : 



The Upper Silurian. — Immediately overlying the Tonto at its outer edge and possibly 

 conformable with it are red to brown fossUiferous coarse-grained lime rocks having a thickness 

 of about 70 feet. They form only a narrow band but are continuously exposed from the Tonto 

 basin to Nantan Mountains, where not covered with talus or lava. The best exposures observed 

 by the writer are on the trail to the Salt springs, some 10 rmles southwest of the farmer's resi- 

 dence on Cibicu, and on the John Dazen trail near the Oak Creek break about a half mile south- 

 east of Oak Creek cliff houses. This formation is Silurian; at least the fossils obtained, Orthis 

 davidsoni, Stromhodes pentagonus, etc., seem to bear out this conclusion. 



I 13. NEW MEXICO. 



Lindgren '*^^ gives the following account of the Silurian of New Mexico : 



The Silurian is recognized at Silver City, at Lake Valley, and probably also at HUlsboro as 

 thin beds of limestone and quartzite, but does not seem to be present everywhere between these 

 places. It lies conformably above the Ordovician and at Silver City can not be differentiated 

 from it. In the Franklin Range of Texas Richardson measured I7OOO feet of Silurian lime- 

 stone. 



I 14. OKLAHOMA. 



The Arbuckle Mountains of Oklahoma comprise Silurian and Devonian strata 

 which were separated by Taff into two mapped formations. The lower formation, 

 the Sylvan shale, is of Silurian age, and the upper, the "Hunton limestone," is 

 of Silurian and Devonian age. The Sylvan overlies the highest known fauna of the 

 Ordovician, yet its fauna is related to the Utica of the New York Ordovician. The 

 "Hunton" contains strata carrying in succession Niagara, Helderberg, and 

 Oriskany faunas. The following is the stratigraphy and paleontology according to 

 Taff and Uh-ichi^"** 



The Sylvan shale and the succeeding Hunton limestone are comparatively thin formations. 

 * * * The nearly pure lime deposits laid down at the close of Viola [upper Richmond, latest 

 Ordovician] time were succeeded by dark-blue to black and green clay in apparently conform- 

 able succession. The deposition of the greenish Sylvan shale continued without interruption 

 untn it reached a thickness of from 60 to 300 feet. * * * 



a Am. Jour. Sci., 4th ser., vol. 21, 1906. 



b Tishomingo folio (No. 98), Geol. Atlaa U. S., U. S. Geol. Survey, 1903. 



