CLINTON CONGLOMERATES AND WAVE MARKS. 57 
it evidently lies upon an eroded base, the underlying sandy-look- 
ing limestone having suffered more or less marked erosion previous 
to the deposition of the crinoidal layer. Owing to the marked 
stratification of the sandy limestone, the irregular erosion of its 
upper surface is readily observed, and the crinoidal layer is seen 
in places to descend considerably below the original level of the 
sandy layer. In some places the sandy limestone has been cut 
through so that the crinoidal bed rests upon the bed below the 
sandy limestone, but in the stretch examined along the river 
front the erosion seems to have been confined chiefly to the 
sandy layer and rarely extends to the layer beneath. Nothing 
could better express the limited vertical range of this erosion. 
In the crinoidal bed occur many fragments evidently derived 
from the sandy layer immediately beneath. Some of these 
fragments are of considerable width, slabs as long as two and a 
half feet having been seen inclosed in the crinoidal layer. The 
thickness of these fragments rarely exceeds four inches and is 
usually less. One slab of sandy limestone must have been at 
least five feet long, but this was exceptional. The usual length 
varies from four to seven, at times twelve inches, and the thick- 
ness varies from one to two inches. The edges are usually more 
or less rounded, but not to the same extent as are the pebbles 
of some of the Clinton conglomerates. Many of these pebbles 
occur near the base of the crinoidal layer; fewer are found in 
the central parts of this layer, but quite a number occur again, in 
places, at thetop. It is very evident in this case, that the peb- 
bles could not have been derived from a distant source, but must 
have been carried to pockets and depressions already formed in 
the sandy layer, while other parts of the same layer, at some 
point in the more immediate vicinity, were suffering erosion. 
Occasionally inclusions are found which were not derived from 
the sandy layer beneath. In one case, at least, a fragment of a 
coarsely crinoidal rock was included in the crinoidal layer; it was 
very similar to the inclosing rock, but its lines of stratification 
had a different angle. Rounded chunks of a clayey substance 
at present hardened, very fine-grained, and yellowish in color, 
