84 THE MOUNTAIN. 



These mountains are often but a few yards wide at their 

 summits, and resemble huge walls in ruin ; their sides the 

 talus of long ages of gnawing by the teeth of time ; but 

 their majestic cliffs, still imperial, proud, and defiant, offering 

 battle, as if forever, to the elements that seek to destroy 

 them. Where the rocks in them have a gentle inclination 

 they are high, attaining the elevation of 1400 to 1600 feet 

 above the waters in the gaps. Where the rocks are in a 

 vertical position, the mountains are low. The cause of 

 this is obvious ; the gently-inclined strata resisting like the 

 slope of a dam, while the vertical rocks had to contend 

 against the direct action of the denuding currents by co- 

 hesion alone, the abrading force operating at right-angles 

 to the resisting surfaces. 



Above, this formation passes by degrees into the super- 

 incumbent formation, showing, as usual, a mingling of the 

 characters of both. 



The philosophy of the structure of valleys of Formation 

 2 surrounded by this rock, will be understood by observing 

 its relation to that Formation, and applying the common 

 laws of natural philosophy. 



FORMATION 5 



Is the next in the ascending order. 



It is composed of a series of variegated slates, shales, and 

 sandstones of all colors, generally light, as olive, yellow, 

 gray, and red In the lower part of the formation the sili- 

 ceous element of the subjacent group mingles, presenting 

 sand strata, which contain fossils, animal and vegetable, or 

 trilobites and fucoides. 



This Formation is always found on the flanks of moun- 

 tains of Formation 4; sometimes making gradual slopes 

 high up the mountains; and again, partially denuded, it 

 gives more precipitous declivities, and is covered by frag- 

 ments of the sandstone of Formation 4. 



This is the formation which contains the celebrated fossil- 

 iferous iron ore, upon which so many furnaces of the State 



