248 Notes on American Geology. 



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 of 

 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 after 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. Fresh- 

 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. Tf there was scarcely any 

 dry land at that period, it follows that the universal 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- 



