40 Feather stonhaugh's Geological Report, 



the others are horizontal. The inference is obvious that some 

 disturbing cause operating from below has thus tilted these 

 beds up, and that it prevailed with greater intensity and con- 

 stancy during the earlier geological periods than it has done 

 since the deposition of the old red sandstone. This striking 

 difference in the position of the planes of mineral beds be- 

 longs to a class of geological phenomena so various and im- 

 portant, that it is proper in this place to mention some of 

 them, that the student, from perceiving how cognate they are 

 to each other, may form his judgment as to the reasonable- 

 ness of the cause to which their common origin has been at- 

 tributed. It will also afford an opportunity of alluding to some 

 complicated cases under which rocks sometimes present 

 themselves, and which, being deceptive, require accurate 

 observation. 



In diagram No. 2, the transverse lines making an angle of 

 45 degrees with the horizon, represent the beds formerly de- 

 posited in a horizontal plane, tilted up. Such rocks are said 

 to dip 45 degrees, and this slope of their planes often in- 

 creases until they are set completely upon their edges, and 

 become vertical or perpendicular. But at whatever degree 

 they may dip, the uppermost edges of the beds thus tilted up 

 always have the same strike or direction. When they dip to 

 the east, their edges of course run north and south. This 

 phenomenon is a source of constant annoyance to those who- 

 travel on wheels in the Shenandoah valley of Virginia, 

 where the roads, running nearly east and west, cross the 

 edges of the upheaved limestone beds at right angles. It will 

 not escape the reader that in countries where the dip, as fre- 

 quently occurs, is constant through a great area of country, 

 the strike of the beds, being known, may be useful to travellers 

 in doubtful cases, and in the dark, in pursuing their course. 



Amongst the instances where a student is apt to be de- 

 ceived by the appearance of stratified beds, if observed at a 

 distance, or whilst rapidly passing them, is that of his being 



