Association of American Geologists and Naturalists. 267 



beneath the sea, appears to me I confess entirely unsustained by that 

 kind of demonstration which so important an inference demands. In- 

 deed the absence of any marine deposit identifiable with the Lake 

 Champlain clays, from levels higher than the beds of the valleys enu- 

 merated, seems a conclusive proof that the only part of the land sub- 

 mersed was in those narrow channels. Thus New England and the 

 mountain region of the Adirondack, were islands separated from the 

 main continent by merely shallow and confined straits. 



This conclusion has reference, however, only to the condition of the 

 land during the tranquil interval between the epochs of vehement ac- 

 tion denoted by the earlier and later drift deposits ; and the main ques- 

 tion still remains unanswered, as to what was the degree of submer- 

 gence of the continent at those periods of commotion. Was " the 

 whole surface" at present overspread with the detrital matter then " per- 

 manently covered by water," as some of our geologists suppose, and 

 the depression therefore greater even than in the quiet epoch which in- 

 tervened ; or do we in reality possess one satisfactory monument to re- 

 Cord that any part ofijgfie surface, at either bowlder period, was below 

 the general level of the ocean. If the presence of marine fossils in 

 the post pleiocene clays is accepted as a convincing argument that the 

 tracts to which they belong were at the time of their deposition beneath 

 the waters of the sea, certainly the universal absence in all other dis- 

 tricts of any analogous remains, is no less conclusive that the submer- 

 ged condition which would have infallibly produced them did not exist. 

 To this reasoning it cannot be objected that the sediments of the sup- 

 posed waters may have been removed by the same currents which 

 brought in the drift ; for the waters of the later and perhaps most dis- 

 turbed of the two drift periods, were manifestly unable to obliterate the 

 limited post pleiocene clays which they overspread and could only par- 

 tially denude. 



4th. Respecting the age of the drift deposits of this continent, I have 

 already presented the chief facts hitherto discovered which seem con- 

 nected with the inquiry. That the whole belongs to a later age than 

 "that of the miocene tertiary, is evident from the superposition to beds 

 of that date in Martha's Vineyard ; and there can be little hazard in as- 

 signing it to an epoch in that relatively recent though vaguely defined 

 period of the tertiary, denominated by Lyell and other geologists the 

 post pleiocene. Commencing before the era of the Champlain fossili- 

 ferous clays, the same energetic and wide dispersion of detrital matter 

 was repeated after hs close, and yet the whole was apparently termina- 



