THE GEOLOGICAL HISTORY OF NEW YORK STATE 69 
raised Cretacic pencplain. This being the case, are any remnants 
of that upraised surface still left? In the affirmative answer to this 
inquiry we have the most positive evidence for the former existence | 
of the Cretacic peneplain. We have said that the most perfect 
development of the peneplain was from central Pennsylvania to 
Virginia, and it is just here where we should expect to find the 
best remnants of that old surface. In this region the typical Ap- 
palachian ridges and valleys, which run parallel to the trend of the 
mountain range, are very well developed. These valleys are the 
trenches cut along the belts of soft rock and to below the surface 
of the upraised peneplain, while the ridges have developed along 
the belts of hard rock and their summits actually represent portions 
of the old peneplain surface. These ridges all rise to the same 
general level for miles around, and as viewed from the summit 
of any one of them the concordant altitudes give rise to what is 
called the “even sky line” which is a most striking feature of the 
landscape. Plate 35 gives an excellent idea of the even sky line 
across these ridges. 
In New York State the concordant altitudes are not so well 
shown both because the peneplain was here not so perfectly de- 
veloped and because the attitude of the strata has largely been 
unfavorable to the formation of long, distinct ridges. Remnants 
of the peneplain are, however, unmistakably present in New York 
as, for example, on a very large scale over the great Southwestern 
plateau whose high points nearly always rise to altitudes of about 
2000 feet. This plateau is simply a part of the upraised and dis- 
sected Cretacic peneplain, and the slight downward sag toward the 
middle (already noted in chapter 2) is no doubt due to a slight 
downwarping of the general level during the process of uplift. 
The topographic map (plate 4) well illustrates the character of 
this dissected plateau. The present elevation of the peneplain 
‘remnants does not necessarily indicate the maximum amount of 
uplift. In the next chapter evidence will be presented to show 
that, for the New York area at least, the land was considerably 
higher in the Tertiary period than it is at present. 
The summit of the Tug Hull province is a small plateau at an 
altitude of about 2000 feet, and is merely a remnant of the upraised 
peneplain which was formerly connected with the Southwestern 
plateau. As one stands at the summit of Tug hill and looks out 
over the western slope of the Adirondacks, he is impressed by the 
remarkably even sky line there shown at an altitude of a little over 
2000 feet. The east-central Adirondacks andthe Catskills present 
exceptions because these regions stood out above the old peneplain. 
