NORTH AMERICA AND THEIR VERTEBRATE FAUNA. 83 



The Round Knob Formation.— This name is applied to the formation previously- 

 called the Pittsburgh Red Shale by I. C. White. A typical section is shown in Madi- 

 son Township, Columbiana County, Ohio, near the cross-roads in section 15. 



"The beds vary from structureless, purpUsh-red clay to deep red even-bedded 

 shale, which may alternate with bluish layers. The more sandy portions frequently 

 show ripple-marks and sun-cracks. Lenticular siderite concretions are common in 

 the bluish shales and nodules of Kmestone and hematite in the structureless red clay. 

 The hematite is in dense, reddish nuggets of submetalUc lustre, which contain 55 to 60 

 per cent of iron and would be of value as iron ore were the quantity greater. Land-slips 

 are common in the Round Knob horizon ; hence the soft red clay becomes distributed 

 over a great vertical range, thus giving an appearance of considerable thickness. 



"There has been much dispute as to the cause of the red color in the 'Coal 

 Measure' beds. That it is in the case of the Round Knob horizon original rather 

 than a secondary phenomenon due to the reactions of weathering is evident, since the 

 redness is persistent where the beds are hundreds of feet below the surface, as is shown 

 by drillings. Such colors are entirely wanting in the lower beds of the Pennsylva- 

 nian series, and appear near the middle of the Conemaugh for the first time. It is 

 true that reddish tints are seen in a few horizons in the lower third of the formation, 

 but these are largely secondary, or, in other words, the result of weathering, and only 

 appear at or near the outcrop. It is probable that the change in cHmate, together 

 with varied sources of supply of the sediments, are largely responsible for the red beds. 



"The Ewing Limestone.^ — Beneath the Barton coal is clay and more or less lime- 

 stone in the form of nodular layers. The Hmestone is much more persistent than the 

 coal and is found nearly everywhere except in places where it has been eroded and 

 its horizon occupied by the sandstone. Ordinarily, there is only a nodular layer a 

 foot or so thick, or a single course of limestone less than 2 feet, but here and there 

 in the eastern part of the State are areas where the limestone attains a thickness of 

 S to 10 feet and consists of a number of layers interlain with clay. * * * 



"Fossils of types generally regarded as fresh- water are abundant in the Ewing 

 limestone. Spirorbis is the most numerous of these, and ostracod carapaces are next 

 in abundance. Fish-teeth are not uncommon and reptilian bones are also present. 



"Along the lower Symmes Creek Valley, in Lawrence County, the Ewing lime- 

 stone is a gray rock in a single layer about 1 5 inches thick. An outcrop on the Alfred 

 Ward farm, near Getaway, was found 51 feet above the Cambridge limestone. In 

 many places to the north there is only red clay with nodular limestone in this hori- 

 zon, or frequently sandstone. In some localities the limestone is so ferruginous that 

 it has been dug for iron ore. 



"A reptilian bone is reported from the same limestone in Harrison County, in a 

 railroad cut about i mile west of the village of Jewett." 



It is evident, from the descriptions given by Dr. Condit of the Conemaugh 

 formation in Ohio, that the conditions there near the close of Carboniferous 

 were in many regards very similar to those of the western deposits and that 

 animal life there would have existed amidst almost identical surroundings. 

 This fact is further emphasized by the similarity in the shading of the lime- 

 stones into sandstones, as described by Condit : ^ 



"The sudden thinning of the non-marine limestones to the southward along 

 the Ohio outcrop is noteworthy. Both the Conemaugh and the Monongahela have 



• Condit, Bull. No. 17, Geol. Surv. Ohio, p. 37. 

 ^ Condit, Ibid., p. 250. 



