THE MOUNTAIN. 83 



FORMATION 3. 



Upon 2 reposes a slate and shale formation. It is usually 

 black, dark blue, sometimes gray, olive, and drab-colored. 

 It is a valuable mass, in some places giving roofing-slate. 

 It also contains sand layers, gray and white, occasionally 

 conglomeritic. 



It is one of the mud-stones of the East, spoken of by Mr. 

 Lyell. It gradually mingles with the formation above and 

 below, in layers of calcareous slate and argillaceous sand- 

 stone. It is filled with fossils in some parts of the mass. 

 Thickness from 200 to 6000 feet. 



FORMATION 4. 



Succeeding the last formation is a sandstone group. It is 

 made up of a series of layers, white and gray, sometimes 

 fine-grained, compact; again coarse and conglomeritic. 

 Many of its layers are full of fossil marine plants called 

 " Fucoides." It is from 400 to 2000 feet thick. 



This is the formation which gives the belt of sharp, sym- 

 metrical Appalachian mountains east of the Alleghany range 

 and which are parallel with it. They run like majestic waves 

 from northeast to southwest in lines as straight for miles, 

 often, as they could be run by the compass. Where these 

 mountains are entire anticlinal axes, they present broad, 

 gentle slopes ; but where the axes are split or cracked open, 

 and the two sides separate to surround valleys of the sub- 

 jacent formations, as around the large limestone valleys of 

 Formation 2, the mountains are narrow and abrupt, with 

 steep and precipitous escarpments, covered with stone slides, 

 and spaces of loose, massive fragments, in rugged confusion, 

 with no vegetation except the lichen and moss. 



The material of this formation being hard and indestruc- 

 tible, the mountains which it always forms run like immense 

 dikes through the country, cut by numerous water-gaps, 

 through which the streams and roads of the region pass 

 from valley to valley. 



