Rocky Mountains* 11 



the rapidity of their currents, render them unfit for the abode 

 of vegetable life, and is incompatible with the existence of 

 putrefaction, notwithstanding the transparency of their 

 waters, and the reddish, or yellowish colour of the rocks 

 which pave their beds, have a tinge of green, like" the Ohio 

 and Cumberland, at times of low water. It is well known 

 that the water of the ocean, though more transparent than 

 any other, is usually green near the shores; and on sound- 

 ings, while at main ocean, its colour is blue. Perhaps the 

 power which transparent waters have of decomposing the 

 solar light, and reflecting principally the green rays, may 

 have some dependence upon the depth of the stratum. If this 

 were the case, we might expect all rivers, equally transparent 

 and of equal depth, to reflect similar colours, which is not 

 always the case.. 



In the southern part of Pennsylvania, the range called par- 

 ticularly the Alleghany ridge, is near the centre, and is most 

 elevated of the group. Its summit divides the waters of the 

 Susquehannah, on the east, from those of the Ohio on the 

 west. 



This mountain consists principally of argillite and the 

 several varieties of gray wacke, gray wacke slate, and the 

 other aggregates, which in transition formations usually in- 

 tervene between the metalliferous limestone and the in- 

 clined sandstone. The strata have less inclination than in the 

 Cove, Sideling, and South mountains, and other ridges east of 

 the Alleghanv. The summit is broad, and covered with 

 heavy forests. Something of the fertility of the Mississippi 

 valley seems to extend, in this direction, to the utmost limits 

 of the secondary formation. The western descent of the Al- 

 leghany ridge is more gradual than the eastern, and the in- 

 clination of the strata, in some measure, reversed. It is pro- 

 per to remark, that, throughout this group of mountains, much 

 irregularity prevails in the direction as well as of the dip 

 and inclination of strata. If any remark is generally applica- 



