104 Feather stonhaugh''s Geological Reporf. 



finds its way to the Potomac. East, however, of this moun- 

 tain is a small ridge, which stops short of Cumberland to the 

 northeast, being divided from its southern portion, which 

 continues its southern course across the Potomac in Virginia, 

 by a basin about a mile and a half wide, in which Cumberland 

 is situated, and through which the Potomac flows. This ridge 

 is composed of shale and limestone, with producta, spirifers, 

 and cardia. It is evident that the ancient floods which have 

 retired from this part of the country at the period of its be- 

 coming dry land, have carried away the subjacent shale, and 

 that the superincumbent limestone has fallen in for want of 

 support. The gorge of Wills's mountain is a very remarka- 

 ble locality ; it extends about 3,000 paces, and is in some 

 places 500 paces wide, presenting a very curious and quite a 

 magnificent section of the mountain. This consists of red 

 shale, subjacent to grayish sandstones and grits. On the north 

 side the summit is about 850 feet from the creek, showing a 

 bold mural escarpment, with an immense talus of fallen 

 masses, extending two-thirds of the way up the cliff". On the 

 south side, at the eastern end, the base rises by a slight incli- 

 nation into a regular curvature of the beds, the lowest being 

 a red shale, and the upper beds consisting of grayish sand- 

 stones and grits. The curvature presents a segment of an 

 arch, the base of which would be about 9,000 feet. On 

 reaching the western end of the gap, I observed that the 

 flexure of the beds had as it were collapsed, and that a great 

 many of them, to the amount of about 200 feet in thickness, 

 were hanging vertically upon the flattened side of the arch, as 

 in diagram 13. Amongst the rubbish I had seen some speci- 

 mens of fucoides AUeghaniensis, and as soon as I fully com- 

 prehended the collapsed state of these rocks, it occured to me 

 that I might possibly find the beds to which they belonged, 

 and climbing the cliff" and looking diligently about, I had the 

 satisfaction of finding them, with several other varieties of 

 fucus in place on the outermost of the vertical beds. The 



