OR UPPER BARRIER. 339 



sand with detached rocks carried to the lower, charac- 

 terize as elsewhere this remarkable tract. 



9. The breach by the Potomac through the Blue 

 Ridge. 



Much might be written on this disruption of the Blue 

 Ridge, or South Mountain, as it has sometimes been 

 called. The great agent was probably the united current 

 af the Potomac and Shenandoah. The mountains have 

 every appearance of having formerly opposed a formida- 

 ble barrier to the accumulated water. Obstructed, as 

 it were by a dam, a pond or lake must have been formed 

 beyond them. Their height is estimated at about twelve 

 hundred feet, or not quite so much. Mr. Volney has 

 incorrectly traced them along to the Catskill mountains 

 of New- York ; whereas they really belong to the Sha- 

 wangunk chain, which is quite distinct, both as to its si- 

 tuation and composition, from the Catskili : the former 

 being composed of quartzy rocks and amygdaloid, and 

 the latter of sandstone. 



The sides and summits of the mountains near Harper's 

 ferry are in summer clothed with green oaks. Chestnuts, 

 maples, and planes are frequent before the eye. The lime 

 tree, the tulip tree, the locust tree, awf the willow tree, 

 overspread the surface with their veraure. While the 

 persimmon, the passiflora, the calycjjtnthus, and the pa- 

 paw, strike their roots through the sands of the shores 

 and the crevices of the rocks. 



The predominating rocks and stones dispersed over the 

 parts of Virginia and Maryland, which lie on both sides 

 of the Potomac between the tide waters of Georgetown 

 and the Blue Ridge at Harper's ferry, are quartzy. 



