280 GEOLOGICAL EXCUB8IOH TO THE ROCKY MOUNTAINS. 



series in the Wills Greek gap a1 Cumberland to the sumniil of the 

 Penno-Carboniferous, or Permian, beds in the middle of the great 

 plateau between the Monongahela and Ohio rivers. 



The character of these several terranes and their thicknesses, etc., 

 along this line, will now be briefly described in ascending order. 



Medina series (IV of Rogers, base of Upper Silurian), thickness 2,056" 

 feet. 



Feet. 



(a) Oneida Conglomerate ' 



(b) Bed Medina 1 - 20,) 



(r) White Medina 50 ° 



The thickness of the Bed Medina and the Oneida beds in the above 

 measurement is based upon data obtained from a deep boring in Wills 

 Creek gap, one mile east from Cumberland. The well starts 790 feel 

 above the base of the Bed Medina, penetrates the Hudson River dark 

 shales at 1,146, and stops in them at 2,010, probably about l.ooo feet 

 from the top Of the Trenton limestone. 



The White Medina is finely exposed in the great arch of Wills 

 Creek Mountain, where its top rises to L,300 feet, almost vertically, 

 above the bottom id" the gorge through which Wills Greek finds an exit 

 to the North Potomac River at Cumberland. 



This great arch dies rapidly away to the northwest and the Medina 

 passes below the surface where the North Potomac passes across its 

 trend L5 miles southwest from Cumberland, but 10 miles farther 

 southwest the arch swells up again, and the Medina coining above the 

 surface makes the summit of New ('reek Mountain. Thisrockis the 

 great mountain-maker of the Appalachian belt east from the Allegha- 

 nies and west from the Blue Ridge, and on account of its hardness is 

 highly valued for ballasting railroad tracks. 



Clinton scries, ( I') thickness 721 ivv\. 



I'Vot. 



(a) Lower olive shales 100 



(6) Iron sandstone 20 



(c) Middles shales and limy beds 300 



(d) Fossil iron ore 1 



(e) Upper limest ones and shales 300 



The Niagara limestone proper has never been differentiated from the 

 great mass of limy shales and Impure limestones which occur in the 

 interval between the Salina series and the Medina sandstone, any- 

 where along the Appalachian system. It is possibly absent, but until 

 the richly fossiliferous beds which are here grouped under the Clinton 

 are thoroughly studied, no one can say positively that the Niagara 

 limestone of the New York column is not represented in the series of 

 rocks given above and all classed as Clinton. 



This series is beautifully exposed at Cumberland, along the Pennsyl- 

 vania Railroad, near the southern entrance to Wills Creek Gap. The 



