of the Northern CatsJcill Mountains. 145 



valley becomes narrower and steeper-sided until, where it 

 enters the Schoharie, it is a veritable canyon, only 3/4 mile 

 wide at the top, with walls TOO feet in height, and is trenched 

 sharply into the 2000 foot plateau. 



A second feature indicating that the plateau is the product 

 of an earlier erosion cycle is well illustrated in the southeastern 

 part of the Cooperstown sheet. The drainage here is what 

 might be described as unilateral — all tributaries come in from 

 the north, while the south walls of the main valleys are 

 practically unbroken. 



This lack of symmetry, it is to be presumed, is a result of 

 the adjustment of the streams to gently dipping rocks. This 

 adjustment must have taken place in a cycle previous to the 

 rather sharp dissection which produced the present topography, 

 for there is no evidence of any considerable down-dip 

 migration of the master streams, or of other adjustments, since 

 this dissection began. 



The plateau appears, therefore, to represent an old age plain 

 or, as some would call it, a peneplain produced during an earlier 

 cycle of erosion and sharply dissected by the streams during 

 the present cycle. 



Grabau* correlates this 2000-foot plateau with the Cretace- 

 ous peneplain. Davisf suggests that the Cretaceous peneplain 

 level in the Catskills lay at about 2500 feet — too high for our 

 2000-foot plateau, and too low for the general summit level of 

 the mountains. Since the precise dating of these physio- 

 graphic features must wait upon more detailed investigations 

 outside of the area under discussion, no attempt is here made 

 to assign a date to the 2000-foot peneplain, or to correlate it 

 with others, further than to state that it apparently continues 

 westward across southern New York. 



What may prove to be evidence of a later period of halted 

 downcutting is found within the Schoharie Valley trench. A 

 rock bench is revealed by postglacial gorge cutting at North 

 Blenheim and Mine Kill at elevations of about 940 feet at the 

 former place and about 1050 at the latter. One and one half 

 miles below North Blenheim also, on the east side of the valley, 

 is a similar rock bench between 900 and 960 feet above sea- 

 level. This may correlate with one of the platforms in the 

 Mohawk Valley— possibly that at 700-800 feet. 



Several pronounced passes or gulfs cut the Catskill escarp- 

 ments. Three of them cutting through the strong Central 

 Escarpment are especially noteworthy. Among the simplest 

 is that through the northeastern escarpment at East Windham. 

 This seems to be a normal stream valley beheaded by the 

 recession of the escarpment, and subsequently smoothed out 

 *Grabau, k. W., loc. cit. fBull. Geol. Soc. Amer., ii, 566. 



