222 The American Geologist. October, 1894 
ern Appalachians.* It forms the even crests and sky-lines of 
the mountainous ridges in Pennsylvania and New Jersey, and 
thence it declines beneath the sea level, forming the plane of 
unconformity between the upturned edges of the Jura-Trias 
or Newark group and the Potomac and higher beds which 
rest upon it. So conspicuous is this feature in the landscape 
of the eastern United States that it has generally attracted 
the attention of observant travellers. Thus, in the valley <>!' 
the Ohio, we find the following description given by Bourne :f 
Perhaps the besl idea of the topography of this region may be obtained 
by comparing il to a vast elevated plain, near the center of which the 
streams rise and in their course wearing down a bed or valley, whose 
depth is in proportion to their size or the solidity of the earth over 
which they flow, so that our hills, with some few exceptions, are noth- 
ing more or less than cliffs or banks made by the action of the streams, 
and although t hese cliffs or banks on t he rivers or large creeks approach 
tlie size of mountains, yet their lops are generally level like the remains 
of an ancient plain. 
N~on-marine beds rest on the peneplain on the Atlantic ('oust. 
It is a curious fact that immediately succeeding the period 
of erosion in which the peneplain was in great part formed, 
there comes, along the Atlantic coast in southern New En- 
gland, New Jersey, and some of the states farther south, a 
series of non-marine beds, the Potomac and the lower portion 
of the Upper Cretaceous or Baritan group in New Jersey. 
These beds preclude the idea of marine erosion as the cause 
of the denudation which preceded them. It was at a later 
time in the Upper Cretaceous that the sea encroached upon 
the area and deposited sands and marls. The Potomac beds 
are referred to the border line between the Jurassic and the 
Cretaceous; and, if we admit their earlier age we must sup- 
pose that the Piedmont portion of the peneplain was essen- 
tially reduced to baselevel before the close of the Jurassic 
period. 
The plant-bearing Raritan clays in New Jersey dip ocean- 
ward, according to Prof. W. B. Clark. J at a rate somewhat 
*Hayes and Campbell, Geomorphology of the Southern Appalachians, 
Nat. (icon-. Mag., vol. \. 1894. 
fQuoted in J. II. Colton's Western Tourist or Emigrant's Guide. New 
York, 1846, pp. 10-11. 
\\ Preliminary Report on the Cretaceous and Tertiary formations of 
New Jersey, Ann. Report X. J.Geol. Survey for 1892 (pub. 1893), p. 182. 
