612 GEOLOGY OF OHIO. 



line of the county. The layers are seldom an inch thick, except when 

 black flint courses, three or four inches thick, come in to supplement 

 the shales. They are almost destitute of fossils ; but three shells have 

 ever been recognized in this series at this point. One of them is a shell 

 of universal occurrence, and that existed as a species through vaster 

 periods of duration than any other known form, viz. : Strophomena 

 rhomhoHalis, Wahl. It begins in Lower Silurian time and continues until 

 the close of the Carboniferous age ; thus spanning the whole vast cycle 

 of Paleozoic time. It is but half grown, as found in the shales, having 

 nothing of the robustness belonging to the form in the beds below. A 

 second shell sometimes, though rarely, found in these beds is Spirifera 

 mucronata, Hall, another form of quite extensive range. The third form 

 noted here is identified by a single specimen only, as Spirifera niaia, Bil- 

 lings. There is no reason to doubt that portions of the series will 

 hereafter be found as rich in fossils as the equivalent beds are elsewhere. 

 The shales are useful only for road-making. The flint that they hold 

 gives some promise of rendering service in this way. They would prob- 

 ably answer a better purpose than the Coal Measure limestones, which 

 have lately been brought into Columbus at considerable expense, for this 

 use. The whole section of the Corniferous limestone is nowhere com- 

 pleted in this locality, the highest beds seen in it belonging to about the 

 middle of the Delaware division. 



The general section shown at the State quarries is represented in the 

 annexed wood cut. As these quarries occupy a large area, and, as the 

 separate layers expand or shrink, or even disappear if they are followed 

 far, many sections can be obtained that will not match in every particu- 

 lar with the one here given ; but the aim has been to show the yield of 

 the quarries where most extensively worked. 



Twenty-six and a half feet are represented in the section. 



The lowest course lies below the level of low water in the Scioto River. 

 It was reached only when the quarries were being worked for the con- 

 struction of the State-house. It is a massive bed, five and a half feet in 

 thickness, though it splits into two nearly equal courses so easily, that 

 it is almost as well to describe it as consisting, normally, of two courses. 

 It can be raised in large blocks, and furnishes the best stone of the 

 quarry for massive work. The columns of the State-house are derived 

 from this layer, split, however, into two, as it generally is when worked. 



Four other heavy courses, measuring respectively two feet ten inches, two 

 feet three inches, two feet six inches, and two feet, come next in order. 

 All are raised in blocks of good size, and all are available for the best 



