. THE ATLANTIC SYSTEM OF MOUNTAINS. 371 
6. The last important elevation known in the White Mountains. The forces caused 
the Helderberg strata to be put into vertical and inverted positions. We have no evi- 
dence illustrative of the Appalachian revolution in the Atlantic district, unless it may 
possibly be represented by the smaller curvatures in the andalusite slates along the 
Mt. Washington carriage-road. Horizontal Devonian sandstones, resting upon inclined 
Helderberg strata along the eastern edge of the Atlantic district in Maine, fully con- 
firm us in the belief that the Appalachian revolution, at the close of the Carboniferous 
period, was principally confined to the formations west of the great valley. 
7. The changes in Mesozoic and Cenozoic times have diminished the size of the 
Atlantic mountains, so that they are scarcely recognizable between Connecticut and 
Virginia. The deposition of the Triassic sandstones would seem to have required a 
depression below the present level. Although no marine fossils occur in them, we 
-must believe the basins to have had oceanic connections. 
8. There must have been an elevation following the Triassic period sufficiently great 
to furnish the barriers for the Lower Cretaceous lake extending from eastern Long 
‘Island through New Jersey and a part of Pennsylvania. The former extension of the 
Hudson river channel 80 miles out to sea may have had some connection with the exit 
of the water from this Cretaceous lake. 
g. A later depression is indicated by the presence of shallow water, Ico miles or so 
in width, between New Jersey and the Great Banks of Newfoundland. (See Pl. I, 
Vol. II.) 
to. There must be added the changes of level described in the glacial and Champlain 
periods. Authors are not agreed as to their extent, while the current of opinion and the 
progress of discovery constantly tend to diminish their magnitude. 
This review of the history of the Atlantic chain enables us to realize its magnitude, 
although the northern and middle sections are now partially submerged beneath the 
ocean. 
APPENDIA. HH. 
THE GEOLOGICAL MAP. 
Not until the last moment has the geological map in the six atlas-sheets been com- 
pleted. There are some small changes upon it from the statements of the text of Vol- 
ume II, which are in all cases improvements. The north-west sheet shows for. Quebec 
the elaborate subdivisions of the Huronian (Quebec), delineated by Sir. W. E. Logan, 
not yet published in the report of the Canadian geological survey, and kindly furnished 
us by A. R. C. Selwyn, the present director. From some familiarity with the country 
south, I have endeavored to carry the same classification into Vermont. I must except 
