248 Notes on American Gieology. 
in Orleans county. They seem to have existed in a small lake, 
in a basin of some primary island, which was finally drained off | 
by no violent current into the sea. This lake probably occurred 
in Canada, since Mr. Hall has clearly proved that the current 
came from the north, bringing with it fine sand, and running 
over a bed of marine shells, (Lingula cuneata,) which were 
moored by their long peduncles in the sand, and therefore all 
range in one direction, nearly north and south, reminding one ses 
boats riding at anchor in a strong tide. 
I am unacquainted with any other trace of ancient fresh-water 
shells in the transition, except in the carboniferous system, where 
Unios are not uncommon ; but it is remarkable that we do not 
find any which existed étear this period, when there was so great 
an extent of dry land, especially in the tertiary epochs, except 
those which Dr. Hildreth discovered in Ohio. ‘These consist of 
ferruginous casts of Unios, approximating in their forms to exist- 
ing species of that region, and have every appearance of being of 
no older date than the upper tertiary ; but it would be wrong to 
give a decided opinion of their age without further investigation 
of their relative position and analogy to existing types. F'resh- 
water shells, found in the calcareous deposits of modern lakes, 
and even where the water has disappeared, and the basins filled 
up with sand, covered by the soil and original forests of the coun- 
try, all correspond with recent species living in the waters of the 
vicinity ; and these marls, and even the monuments of filled up 
lakes, are common throughout the state-of New York. 
‘One of the most interesting features of the transition is derived 
from the ripple marks, which are generally most conspicuous on. 
the sandstones, but occur also on the slates ; one of the most 
beautiful examples of this action of the waters in shoal places 
upon the unconsolidated materials of rocks, may be~seen at the 
slate quarry on the Delaware river above Easton. The stratum 
dips at a considerable angle. Such appearances are common in 
Europe, and have been noticed in New York, Pennsylvania, Vir- 
ginia, and Ohio.. They are records of the ancient condition of 
the globe, not easily misinterpreted. If there was scarcely any 
dry land at that period, it follows that the univérsal ocean was 
very shallow, its bed even, and the currents, except during the 
oscillations of the crust, by no means violent ; hence, in their 
course over incoherent sand, they left their impress upon it so dis- — 
fo« 
