ICE-SHEET EROSION IN NEW YORK 55 



removal of the Clinton along the escarpment and a furrowing of the soft 

 Medina with "a general reduction of the surface to the extent of 40 or 

 50 feet, and the amount may have been considerably greater." When 

 we consider that whatever removal is admitted must include the weath- 

 ered and loosened material, it makes a poor showing for ice erosion. 



Since Doctor Gilbert, with his long experience and wide observation in 

 the field, with his special interest in glaciology, and with his command- 

 ing ability, can give the erosionists no better support from direct evidence 

 than this, they certainly have a very weak case. The statement is again 

 pertinent, that no good example of deep erosion has ever been proved. 



EFFECTS IN THE FINGER LAKES REGION; CENTRAL NEW YORK 



General description. — The topography of central New York has long 

 been known as striking in relief, peculiar in form, and puzzling in origin. 

 A series of deep valleys, with a north and south direction and a north- 

 ward pitch, holds a series of lakes having a digitate arrangement, of 

 which Seneca and Cayuga are the central and larger members (see map, 

 plate 21). These valleys are excavated in uppermost Silurian and De- 

 vonian strata which are practically horizontal, but with a low southerly 

 dip. Several of the valleys do not hold lakes. The valley walls are 

 decidedly convex, and sometimes conspicuously smooth in general view, 

 and southward toward the valley head are generally steep. 



The intervalley ridges are broad, rounded remnants of the north-facing 

 slope of a dissected plateau (the Allegany cuesta), with an altitude at the 

 north ends of about 500 to 800 feet above sealevel. Southward the 

 ridges rise in 20 to 40 miles to about 2,000 feet, the higher strata being 

 Portage-Chemung sandstones. 



The two larger valleys, holding Seneca and Cayuga lakes, have received 

 most attention from writers and have been specially quoted as examples 

 of deep ice erosion. But any sound theory for the genesis and history 

 of these two valleys must also explain all the parallel valleys, from the 

 Genesee on the west to Chittenango on the east; they all belong in one 

 category and have practically the same history. 



Another remarkable set of large valleys, which have not received much 

 attention, are discordant in direction, and probably in altitude, with the 

 north and south valleys. They have a general direction northeast and 

 southwest, and intersect the north-south valleys. The most northerly 

 example extends from the present head of the Onondaga valley, at Tully, 

 northeast past Apulia and Fabius to the limestone valley near Delphi. 

 Another one extends from the Cayuga valley at Ithaca northeast past 

 Cortland and Truxton to the limestone valley at De Ruyter. Still another 

 intersects, near their heads, the valleys of Canaseraga, Hemlock, Honeoy e, 



