OR UPPER BARRIER. 341 



eutiar composition of the strata can be examined to more 

 advantage than under most other circumstances. The 

 rocks may be referred by the modern geologist to the 

 TRANSITION order. At the gap there is scarcely any mica 

 to be seen ; but the quartz is abundant. The structure of 

 the mountain may be comprehended under the following 

 mineralogical disposition. First, quartzy rocks by them- 

 selves, with very little admixture. Sometimes large and 

 milk-white or snow-white masses make their appearance 

 in other strata. Secondly, quartz blended with shist or 

 slate. Both the materials are distinct, and they make 

 coarse associations. The quartz is compact, granular, 

 white, semi-transparent, cellular, ragged, and of various 

 other qualities; but not often crystallized. The slate is 

 of different hues, from pale to brown, greenish and 

 black. Thirdly, quartz and hornblende. The material 

 which I take to be hornblende, is of a brownish and fre- 

 quently of a somewhat greenish hue, and mingled inti- 

 mately throughout with the quartz. This composition 

 appears to me to resemble, more nearly than any thing 

 I recollect, the rocks at the upper falls of the Mohawk 

 river. The hornblende is not known to be distinct, 

 fibrous or crystalline. Fourthly, quartz and iron. Very 

 commonly the quartz is coloured by a ferruginous tinge, 

 and assumes therefrom a brown, reddish or rusty colour, 

 and imparts the same to the other ingredients. Fifthly, 

 quartz and feldspath ; though this mixture occurred so 

 rarely, that it is but barely worth the mentioning. Sixthly, 

 quartz filling the veins and seams of all the other rocks, 

 and giving them stripes or bands of clear white, and 

 sometimes marking them with fantastic flourishes. 



Such are the principal materials and their combinations 

 at the Blue Ridge, where the waters penetrate it, on the 

 territorial line of Maryland and Virginia. Put the mo- 



