DEVONIAN. 273 



maps, but among the settlers it is called Shell Mound, because of its numerous shell fossils. 

 The formation is Devonian, as is indicated by the fossils obtained, Orthis livia, Spiriferfomacula, 

 and Acervularia davidsoni, and corresponds very much to the Devonian formation at the falls 

 of the Ohio. 



I 12-13. SOUTHWESTERN NEW MEXICO. 



At Kingston, N. Mex., in the southwestern part of the Territory, Gordon 

 and Graton ^''^ obsei"ved the occurrence of Devonian limestone similar to the Ouray 

 limestone of Colorado. The fauna of the Ouray has recently been figured and 

 described by Kindle. ^"^ Lindgren ^'^^ states: 



The Devonian is present in an area extending from the Mimbres Mountains westward to 

 the Arizona line and everywhere appears as a thin formation of dark clay shales, usually 

 calcareous in the upper portion. The maximum thickness (465 feet) was noted at Silver City. 

 In the Mimbres Range, where Gordon has given the name Percha shale to the formation, it 

 is only 200 feet thick and its upper part contains a rich and characteristic Devonian fauna. 

 The Devonian is not present in the Franklin Mountains of Texas but appears with a thickness 

 of 200 feet at Clifton, Ariz. The Devonian shale is believed by Gordon to overlie the Ordovician 

 limestone with an unconformity of erosion, but the shale and underlying limestone are con- 

 formable at Georgetown, Lone Mountain, and Silver City, and also at Clifton, Ariz. At any 

 rate the Devonian period in southern New Mexico was characterized by shallow muddy 

 deposits, uniform over a large area. 



I 14-15. SOUTHERN OKLAHOMA. 



Taff and Ulrich *''*° distinguished " Siluro-Devonian " and late Devonian and 

 early Carboniferous strata in the Arbuckle Mountains. The "Siluro-Devonian" 

 rocks were mapped as the "Hunton limestone" and include strata which carry 

 faunas ranging from Clinton to Oriskany. (See pp. 228-230, Chapter V.) The late 

 Devonian and early Carboniferous strata are the Woodford chert, which is 

 described as follows: 



Excepting the flinty Oriskany limestone occurring iOcally at the top of the Hunton lime- 

 stone and possibly the Helderberg member of the latter, Devonian rocks in the Arbuckle region 

 are limited to a single formation of chert and black shale, known as the Woodford chert. While 

 this chert is apparently conformable with the limestone below in any single locality, it appears 

 that this is not true in a broad sense. The Oriskany beds at the top of the Hunton limestone, 

 consisting of several feet of cherty limestones, are present in one place but do not occur in another. 

 In the northeastern part of the uplift, notably near Franks, cherty hmestones are present at the 

 top of the Hunton. Near the western end of the uplift, on the southern side of the Washita 

 Valley, this upper member of hard limestone is absent and the thickness of the entire formation 

 is reduced to a little over 100 feet. In all places there is an abrupt change in sedimentation 

 from the top of the Hunton limestone to the chert or shale of the Woodford formation. 



The Woodford chert has an estimated average thickness of 650 feet. It varies somewhat 

 in Uthologic character. In places massive chert rests upon the limestone ; in other places black 

 shale occurs at the base of the formation. As a rule, however, the formation becomes less cherty 

 from the base upward. It is usually even bedded, occurring in layers from a few inches thick to 

 tliin laminae. In places, especially in the northeast side of the uplift, the formation is composed 

 almost entirely of tliin, fissile siHceous and distinctly bituminous black shale. In this part of 

 the region, a few miles west of Hunton, lentils of almost pure flints were noted interstratified 

 with the black shale near the base. In the western part of the region bluish shales were seen 

 48011°— 12 18 



