238 R. S. TARR — DRAINAGE FEATURES OF CENTRAL NEW YORK 



erosion, it would seem certain that ice erosion in less favorably situated 

 valleys could not have been great. Furthermore, some of the best 

 instances of " through valleys " are south of the zone of most active ice 

 erosion and in a region where residually decayed rock abounds. 



The great number of instances of lowered divides and steepened slopes, 

 in valleys of all sizes and extending in all directions, would demand an 

 altogether remarkable irregularity of ice movement. This may be illus- 

 trated by the case of the Chemung west of Elmira (see plate 40). To 

 account for its lowered divide, ice would have to move either east or west ; 

 but at the end of its narrow section, 2 miles southwest of Elmira, are two 

 small hills with valleys similar to that of the Chemung, one extending 

 north and south, the other east and west (see plate 41, figure 1). These 

 three valleys are apparently of the same origin, for, barring size, their 

 characteristics are essentially the same. To account for them by ice 

 erosion would require ice movement in two valleys at right angles and 

 all within an area of a square mile. 



The flaring of the valleys in two directions from a narrow central por- 

 tion hardly seems a probable result of ice erosion. In Texas hollow, 

 for example, the same characteristics of valley wall form extend both 

 north and south of the narrowest part. It is a question whether, in the 

 case of ice passing through a narrow divide gap, its movement would 

 not be checked by the narrowing valley and a tendency toward stagnant 

 conditions be brought about. Especially would this seem to be the case 

 where the valley extended at an angle to the general ice motion, as was 

 the case in a large number of instances in this region, including Texas 

 hollow. 



There are some cases where ice erosion by the Wisconsin ice sheet is 

 entirely out of the question. This is best illustrated in the Tiougnioga 

 valley, where, on each side of the narrow gorge portion, there is a condi- 

 tion of hanging valleys with gorges in their bottoms, which were devel- 

 oped before the Wisconsin ice advanced. In the Willsey ville and Cay ata 

 valleys also there are tributary valleys developed after the lowered divide 

 conditions were brought into existence, and therefore, since they are 

 drift filled, before the last ice advance. Since this has been proved to 

 be true of several valleys, it seems probable that it is true also of others, 

 concerning which such definite proof has not yet been found. 



Altogether the facts weaken the ice-erosion hypothesis, and in some 

 of the valleys the evidence is definite that their condition is not due to 

 ice erosion during the Wisconsin ice advance. Facts have not been dis- 

 covered which disprove the hypothesis that these valley conditions are 

 due to an earlier ice advance j and, although no evidence of such earlier 



