x8 9 i.j 
321 
[Davis. 
been a run- way of a great ice-current, constricted between the 
highlands on the east and west ; and naturally gaining increased 
power of erosion and transportation with its increased velocity. 
Yet, although more destructive than usual, it would not be safe 
to infer that the detail of topographic form over the valley low- 
land is of glacial origin ; the occurrence of well opened transverse 
notches and water-gaps in the longitudinal ridges indicates that a 
large share of preglacial form is preserved to us. 
Aqueo-glacial gravels are as inconspicuous as deposits of till on 
the rolling lowland west of Catskill ; but they are seen in the 
Catskill trench, by the village, under the clays described in the 
next paragraph. One of the gravel beds, excavated for road 
making, in the bottom of a clay pit on the west side of Catskill 
creek just south of the iron drawbridge, shows a distinct normal 
faulting of its beds near its sloping margin ; and this faulting ap- 
pears to have taken place before the present cover of clays was laid 
over the gravels. This suggests a relationship of the gravels to 
eskers, in which faulting is common ; it being regarded there as 
the result of the withdrawal of the enclosing walls of ice, between 
which the gravels were laid down. The gravels in the pit here 
mentioned do not rise more than forty or fifty feet above tide- 
water. 
The blue clays, shaded with horizontal lines in figs. 1 and 2, 
weathered yellowish near the surface and overlain by a thin de- 
posit of fine sand, occupy the river and stream trenches to a height 
of 130 to 150 or even 180 feet over tide-water ; the greater height 
being towards their lateral margins away from the deep Hudson 
trench. These belong to the immediately post-glacial or Cham- 
plain period, as named by Dana. Their sandy surface forms 
broad even fields, nearly always cleared and cultivated, while the 
isolated ridges of Hudson river sandstones that rise to a little 
higher level are commonly left wooded. The clay flats maybe 
followed up the trenches of the larger streams, such as the Catskill 
and Ivaaterskill ; and in the longitudinal Marcellus valley, above 
mentioned, they are extensively developed ; indeed, it is only 
here and there that the weak Marcellus shales are now seen be- 
neath the clays. The clays are well bedded, very fine and tough, 
without fossils as far as my search has extended ; but I believe it 
is in similar clays that the bones of cetaceans have been found 
imbedded farther north. They are extensively worked near the 
21 MARCH, 1892. 
PROCEEDINGS B. S. N. H. 
VOL. XXV. 
