Davis. | 
330 
[Nov 18, 
three inches in diameter, black, gray, or white ; and occasionally 
small Spirifers with long wings lie among the pebbles ; these be- 
ing the only fossils seen in the ledges. The Hamilton sandstones 
elsewhere seen along the valley walls are barren, often cross- 
bedded, with shaly beds generally of reddish color. Their dip 
decreases to the west, and near Cairo the beds lie almost hori- 
zontal. 
Passing from the foot-bridge southward, one soon rises to the 
level of a stretch of flat fields, ‘220 feet above tide, all pebbly 
on the surface : but these small pebbles are unlike the coarse cob- 
ble-stones on the delta flats above Cairo. The pebble-fields may 
be traced to their margin against the valley walls on the south, 
as at the toll-gate, T, fig. 3, a mile west of Leeds, and nothing 
like a river deposit is to be found above them ; I therefore sup- 
pose that they mark the highest level of the valley deposits at 
this point ; and that their pebbles correspond to the sands that lie 
on the estuary clays, marking a time of rising land and shallow- 
ing waters. The pebbles rapidly become finer and the surface of 
the flats descends on going down stream, and when the beautiful 
Marcellus valley 1 is reached (M, fig. 1), between the Hamilton 
bluffs and the Helderberg limestone ridges, the level of the sand- 
covered clay fiats is only about 180 feet. Near the Hudson, the 
clay fields are thirty to fifty feet lower. The excavations made by 
the Catskill in terracing its old valley-filling are so extensive near 
Leeds that the pebble-flats by Salisbury Manor cannot be traced 
continuously to the clay-fiats of the Marcellus valley ; but to the 
eye, one seems to descend into the other. 
4. Although the valley-filling is now deeply terraced, one can- 
not doubt that when the land rose and put a stop to the estuary 
stage in the history of the Hudson valley, the Catskill trench 
was filled from side to side with sands and pebbles up to the 
height of the cobble- and pebble-fields that now remain in frag- 
ments on its enclosing slopes. Estimating the distance from 
Cairo to the Marcellus valley at five miles, the breadth of the 
valley at the level of the pebble* and cobble-fields at three-fourths 
of a mile on the average, and the depth of the filling at the 
moderate measure of 150 feet, it appears that the amount of 
1 There is no local name for this well-marked topographic feature, nor for the notched 
range of Hamilton bluffs next west of it : I have therefore called them after the rocks 
by which they are determined. 
