584 FRANK CARNEY 
sure is skirted by the highway and is in sight of the New York Central 
Railroad at Keuka Mills. Here the superjacent Wisconsin is the 
thinner, measuring a little less than 18 feet, while the bluish till meas- 
ures nearly 30 feet. The ease with which the former weathers is 
demonstrated by the low angle of slope, and by the covering of vegeta- 
tion; the older drift has a steep slope and no vegetation (Fig. 4), and 
shows very slight evidence of structure. 
The outlet of Keuka Lake drops 265 feet in its course of scarcely 
7 miles to Seneca Lake; it consists of a rock-bound gorge alternating 
with amphitheater expansions, in which one or both of the rock walls 
are absent where the present course crosses or enters a former more 
mature valley. The older drift is noted particularly in these amphi- 
theaters of the present channel. It is probable, therefore, that the 
Keuka basin was tributary to the Seneca basin long before the period 
of bluish-till glaciation. 
This same relationship of drifts is noted in the erosion channels of 
streams tributary to the Keuka Lake Outlet. Along the lateral from 
the south coming in at Milo Mills, the older drift, where not very 
coarse, shows a tendency to lamination, the result apparently of exces- 
sive pressure. We have noted the same condition in other localities 
of this region. 
The most persistent expression of this bluish drift is found in the 
Keuka Outlet valley, which is transverse to the direction of ice-move- 
ment. The valley is very mature. Naturally the Wisconsin ice- 
sheet did less corrasive work here than in the arms of Keuka Lake. 
Erosion and color.—Furthermore, the line of contact of the two 
drifts in the exposure about Dunning’s and about North Crosby 
gives a suggestion as to the manner and amount of the erosion. ‘The 
former contact is about 65 feet above lake-level; the latter, about go 
feet. In east-west cross-section the contact line is a series of sags and 
swells, or anticlines and synclines, presumably parallel to the direction 
of ice-progress, indicating its tendency to groove or plow the subjacent 
surface. 
The color of this old drift is strikingly blue in contrast with the 
adjacent yellowish Wisconsin deposits, and the color persists even in 
the detached masses that are seen in exposures of the recent drift. 
It apparently is not the result of post-Wisconsin alteration; the till 
