Wave-cut Terraces in Keuka Valley 
39 
The resemblance, however, leads to confusion only when the plane 
of the lake surface coincides with, or is parallel to and vertically 
within a few feet of, the hard layer or horizon of rock which marks 
the bench; such a ledge, in the absence of a terrace or other evi- 
dence of a beach, cannot be defined finally as a wave-cut cliff. 
The attitude of a bench resulting from weathering, in reference 
to the horizon, depends upon the dip and strike of the hard layers; 
because of this fact, it is not difl&cult to distinguish the wave-cut 
cliff, except when the bench is discontinuous, showing only in short 
segments, a condition not unusual in the coarse sandstone hori- 
zons because of the horizontal variations in texture. 
2. Streams held against a slope, or against a rock salient, by 
ice, often form a bench somewhat simulating a wave-cut terrace 
and cliff. Such benches have been investigated by Fairchild,^* 
who shows how the banks of glacial drainage streams differ from 
the wave-cut cliff. The latter is not so localized as the former, nor 
in general, so marked in development. ,, 
Considerable effort was devoted to explaining the terraces in 
question as the result of differential weathering. The other 
explanation, ice-stream work, was easily eliminated. The third 
interpretation, discussed in this paper, suggested itself after it 
became apparent that neither of the other two was pertinent. 
STRATIGRAPHY OF BLUFF POINT.^^ 
The succession of formations as given in Bulletin loi of the N. Y. 
State Museum (which appeared after the close of the field season 
during which this study of wave-cut terraces was prosecuted), a 
report prepared by Luther, has been used by the writer in check- 
ing up his field notes on the stratigraphy of the area involved; 
these notes concern only the lithological aspect of the formations 
exposed, and since the slopes of Bluff Point are rather sharp, the 
rock section is almost complete. 
G. K. Gilbert, Bulletin Geol. Soc. Jm., vol. viii, p. 285, 1897. 
N. Y. State Mus., 22 d Rep. of State Geologist^ pp. r23-r30, 1902. 
Ibid., 2 lst Rep. of State Geologist, pp. r33-r35, 1901. 
The Penn Yan Quadrangle will serve as an index map for this region. 
