THE GEOLOGICAL HISTORY OF NEW YORK STATE 63 
figure 20, the molten rock sheet first broke through the strata and 
then crowded its way along parallel to them. During the process 
of cooling there was contraction which expressed itself by breaking 
the rock mass into great, crude, vertical columns, and hence the 
origin of the name “ Palisades”’ (see plate 34). At the base of the 
Palisade rock, as well as on its top a little back from the edge of 
the cliff, the Newark sandstone outcrops. The steep cliff is due to 
the fact that the hard igneous rock is much more resistant to erosion 
and weathering than the sandstone above and below it. 
The rocks of the Newark series are nearly everywhere some- 
what folded, tilted and extensively fractured by normal faults. Just 
when this deformation occurred is not exactly known, but it was 
probably at the close of the Triassic period as will be shown under 
the next heading. 
Briefly summarized, the Triassic was a time of accumulation of 
thick deposits of red sandstone and shale of nonmarine character 
im troughlike depressions along the Atlantic slope, these deposits 
bemg represented in southeastern New York. During their forma- 
tion there was considerable igneous activity when sheets of lava 
- were forced through or between the strata as is well shown in the 
case of the rock of the Palisades. 
JURASSIC” PERIOD 
No rocks of Jurassic age occur within New York State nor as a 
matter of fact in all eastern North America, except possibly some 
fresh-water deposits along the Potomac river of Maryland. The 
failure of such strata is readily explained by the fact that the 
Jurassic period was ushered in by a slight upwarping (accompanied 
by faulting and tilting of the rocks) of the Atlantic border of North 
America so that there were no basins of deposition within the 
present eastern border of the continent. That this uplift actually 
occurred and that the Jurassic period in the eastern United States 
was a time of extensive erosion, is well established because the 
whole Atlantic seaboard, including the tilted and faulted Triassic 
strata, was worn down well toward the condition of a peneplain 
and the next sediments (Cretacic) were deposited upon the eastern 
portion of that worn-down surface (see figure 22). For instance, 
on Staten island and in northern New Jersey, the Cretacic beds 
may be seen resting directly upon the deeply eroded Triassic rocks, 
and hence the proof is conclusive that during much if not all of the 
Jurassic period active erosion was taking place, and this in turn 
implies that the Triassic beds were well elevated in the early 
Jurassic. 
