PENNSYLVANIAN. 459 



as the Ouachita area as a whole has a width of about 70 miles, it is evident that the total short- 

 ening has been very considerable. The rocks appear to have been pushed from south to north. 



Stratigraphically the upper part of the series of rocks is similar to the series in the Arkansas 

 River valley, from the Caney shale upward. The lower part of the series differs from the 

 adjoining rocks in the Arkansas area in the presence of a great thickness of sandstone and shale 

 resting on the Ordovician rocl^ and belonging beneath the Caney shale and apparently above the 

 Y/oodford chert. These have been estimated by Ulrich to have a thickness of 14,000 feet on 

 Little Missouri River. This series was named by Taff'™ the Standley (now spelled Stanley) 

 shale and Jackfork sandstone. At the west is the Caney shale, supposed to be later than the 

 Jaclifork. To the east the Caney shale has not been recognized, and the Atoka formation 

 overlies the Jackfork. In the Atoka folio TafI gives the Jackfork sandstone and the Stanley 

 shale a thickness of 5,000 feet each. Branner °° gave these beds, including the Atoka, a thickness 

 of 18,480 feet in the area west of Little Rock. Purdue,°^°* in a paper on the Arkansas slate area, 

 gives the thickness of the Atoka, Jackfork, and Stanley as 6,000, 6,600, and 6,000 feet, respec- 

 tively, or a total of 18,600 feet, in substantial agreement with the earlier estimate of Branner. 



The age of the Jackfork sandstone and Stanley shale is still a matter of some doubt. They 

 are either late Mississippian or early Pennsylvanian, possibly passiag from the one over into the 

 other. 



The proper correlation of the Caney shale is also a matter of some douot. In folios 74, 79, 

 and 98 of the Geologic Atlas of the United States the Caney was assigned first to the "Carbon- 

 iferous and probably Devonian" and later, on the evidence of fossils which were thought by 

 Girty to indicate a late Mississippian age, to the Mississippian. Two years later (1905) Girty ^''"' 

 placed the Caney in the Pennsylvanian because, inasmuch as it was underlain by 10,000 feet of 

 Carboniferous strata, there was reasonable doubt of its Mississippian age. In 1909 the same 

 author ^'° published a description of the Caney fauna in which, after citing the inconclusive 

 paleobotanic evidence, he summed up the f aunal evidence as follows : 



"The faimal evidence furnished by the Caney is much more extensive than that of the 

 fossil plants referred to above. The Caney fauna has a facies widely different from that of the 

 typical upper Mississippian faunas, and it would be difficult to determine its position in the 

 time scale were it not that it is closely related to certain faunas in Arkansas which contain 

 more of the typical upper Mississippian species and which have long been regarded as belonging 

 to that period. When I originally determined the Caney as neo-Mississippian, I did so because 

 its fauna was so closely allied with that of the Moorefield shale of Arkansas. If, upon returning 

 to the subject with a presentation of one side of the evidence upon which this conclusion was 

 based, it were possible to say that the preliminary opinion had been erroneous, it would afford 

 me real satisfaction as opening a way out of the present difficulties. But a more detailed study 

 of the one fauna and a hasty review of the other have only added to the weight of the evidence. 

 A large number, and those in many cases the most striking and typical of the Caney species, occm- 

 also in the Moorefield shale. * * * 



"The ordinojy inference from these facts, one which I should draw without hesitation were 

 it not for the bearing of the plant evidence found in the Standley, is that the Caney and the 

 Mooreiield-Fayetteville beds were contemporaneous in a geologic sense." But this, it may 

 be urged, does not necessarily entail the Mississippian age of the Caney without carrying 

 the inquiry one stage further. Careful consideration has been given the hypothesis that the 

 Moorefield-Fayetteville beds may be not Mississippian but Pottsville in age. While some cir- 

 cumstances lend a color of probability to such an hypothesis, the negative evidence seems at 

 present to warrant its rejection. 



"If then the Caney correlates with the _Moorefield, if the Moorefield is of Mississippian 

 age, if the Caney rests on the Jaclcfork sandstone, and if the evidence furnished by the Standley 

 flora halts between upper Mississippian and Pottsville, the conclusion that the Standley is 

 upper Mississippian and that the sedimentation of that period was peculiar and excessive in the 



"The White Pine ahale of Nevada, which is also a black shale formation, likewise contains a fauna similar in 

 many respects to that of the Caney. 



