Feather stonhaugh^s Geological Report. 



41 



led to suppose he is among the secondary beds, whilst in fact 

 they are highly inclined. He may be passing an escarpment 

 from the north, where the stratification, as in diagram No. 3, 

 appears to be horizontal, whilst in truth it may be highly 

 inclined : therefore, if, whilst in a region where the beds have 

 a constant dip, he should unexpectedly come to a section of 

 them where they appear to be horizontal, it is always best to 

 stop and examine with some care, as, at some turn of the 

 line, or perhaps by partially uncovering them, he may dis- 

 cover that the strata have a considerable dip, as is exhibited 

 in the diagram.* 



The valley of the Potomac exhibits a great number of in- 

 structive phenomena connected with the dip of rocks, which 

 furnish examples, upon a very large scale, of the singular 

 manner in which the causes to which they may be attributed 

 have operated upon the whole line from the southeast edge 

 of the great western bituminous coal field to Georgetown, in 

 the District of Columbia, a distance of two hundred miles, 

 and a still greater distance north and south of the valley. 

 All the beds, with unimportant exceptions, seem to be dis- 

 posed into anticlinal and synclinal lines. f But of these I 

 shall give some interesting instances when I come to speak of 

 my excursion up that valley on my way to the Northwest 

 Territory last summer. 



* At the top of Cacapon mountain, about ihree nailes fronn Bath, in Morg;ui 

 county, Virginia, there is a remarkable localily called Prospect Rock." 

 From the summit of this escarpment there is a very extensive view of the 

 course of the Potomac river across the inclined beds of the country from the 

 great Alleghany mountain, where the bituminous coal measures begin. On de- 

 scending to the foot of this chfl", and standing in front of the escarpment, the 

 beds appear horizontal ; but at the pass which leads down from the top, they 

 are seen to be tilted up about 18 degrees. 



f The first of which terms is used to express a line created by a dip of 

 the same beds in opposite directions. Thus, a set of beds which in one part 

 of a given area of country whose general planes are horizontal, and which 

 lie as at A, in diagram No. 4, might, in another part of the same area, take 

 the form of B, which is antichnal. 



