448 A. Guyot—Physical Structure and Hypsometry 
bend westward of the whole system, in Pennsylvania, as well 
as the significant fact that it is in the prolongation of the axis 
of that convexity that the western plateaus beyond swell to 
southwest and south; and hence, perhaps, their superior 
said to be, far from coinciding with the chains and valleys, 
they cross them almost at right angles, and were p 
posterior to the scooping out of the valleys and mountain 
chains, on the conformation of which they had so little e 
hey were the last effort of the forces which have sha 
the main Appalachians. f 
A hypsometric feature which may refer to this order 0 
facts is that the three maxima of altitudes, above 4000 feet, 
the Slide Mountain, Hunter Mountain and Black Dome, are 
situated in a straight line, trending from southwest to northeast. 
The short descending plane from this line eastward, which 
