446 A, Guyot—Physical Structure and Hypsometry 
in regard to the main chain, as Table Mountain and Peak-o’- 
Mouse are at the east end, south of the Slide; and both groups 
are of the same elevation. The Graham Mountain group is a 
remarkable hydrographic center sending many branches to the 
Delaware; the Drybrook and the Millbrook to the north and 
west ; the Beaverkill and Navesink west branch to the south- 
west and south. Graham Mountain is also the head of a long 
ridge in which reappears the normal trend of the Appalachian 
chains, which is also indicated by the course of the Navesink 
and of the upper Rondout Creek. But all that region lies 
beyond the pale of my observations and requires further inves- 
tigation. 
What was said above of the Geological structure of the 
we reconstruct in imagination the original plateau from 
which these orographic features have been sculptured, by pass- 
ing a plane through the principal heights, we shall find a law 
very much like that observed in the Northern Catskills. From 
High Point, at the eastern border of mountain land, 3098 feet, 
the plane passing through Lone Mountain, 8670, reaches in the 
Slide its maximum, 4200 at 7 miles, one third of its total 
length. It thence descends more gradually through the Eagle 
Mountain, 3500 feet, down to Belle Ayre, 3400 feet, 14 miles, 
or two-thirds of the entire distance. 
hy it is that, notwithstanding the similarity of general 
structure, the streams in the Southern Catskills should have 
taken an opposite course and shaped themselves into an entirely 
different system, is not easy to say. The absence of border 
chains and of the eastern projection, so characteristic of the 
northern group, may partially account for this difference. 
Primitive, and perhaps later, dislocations, even when 10 the 
shape of simple cracks, may have had a share of influence 1D 
bringing about the result. Traces of the great diluvian gla- 
ciers are found in abundance throughout the Catskills; but 
have seen, in Switzerland, too much of the action of glaciers 
on the ground over which they move, to attribute to that sr 
of geological agencies any great influence on the fundamenta 
features of the present topography of the mountains. 
[am fully aware that to solve such problems and answer the 
