HARSHBERGER : PHYTO-GEOGRAPHIC SKETCH 127 
6. The Pensauken submergence and the deposition of the 
Pensauken formation. 
7. The post-Pensauken uplift and the erosion accomplished 
between this uplift and the last glacial. epoch. 
8. The last glacial epoch. 
During the Pensauken submergence the land was depressed 
to such an extent as to drown the Delaware river at its lower 
end, allowing the sea to pass up its valley and over the peneplain 
which had been developed during the previous cycle of erosion, 
so that a broad sound was formed which connected Raritan bay 
with Delaware bay. The Delaware river entered the Pensauken 
sound at Trenton, and the Schuylkill river, Cobbs, Darby, Crum, 
Ridley and Chester creeks emptied into this sound, having their 
lower portions drowned through this submergence. 
The mouth of the Delaware river during the post-Pensauken 
uplift was transferred to Delaware bay, the creeks above men- 
tioned assumed their old relationship to the country and began 
again actively to erode their basins. This cycle of erosion lasted 
until the ice of the last glacial epoch invaded the northern portion 
of the state. The topography of the region under consideration 
was changed but little and what changes were brought about were 
due to the deposition of drift, which was far from uniform.” 
These topographic and geologic facts have been mentioned 
somewhat at length, because they have strikingly influenced the 
vegetation of the country since Cretaceous times, when we have a 
great and sudden inswarming of the higher plants of modern 
types, at the close of the lower Cretaceous. The great feature of 
this period was its dicotyledonous forests. Thus the following 
genera of trees found in southeast Pennsylvania to-day date from 
the Cretaceous period : Fagus, Liguidambar, Liriodendron, Salix, 
Quercus, Castanea, Betula, Alnus, Platanus, Sassafras, Diospyros, 
Juglans and Hicoria. The botanical character of the Amboy 
Clays of coastal New Jersey, influenced by the changes of elevation 
described above, will be seen from the following brief synopsis.t 
* Gf. Salisbury, R. D. The physical geography of New — Geol. Surv. 
Jeg 1898, — Heilprin, A. Town geology. — Leslie, PY. Final report, om 
Geol. Suet, Rand, T. D. Notes on the geology of southeastern Pennsylvania. 
Proc. Acad. “Nat, Sci. Phila. rg00: 160-338. 1900. 
t Dawson, J. W. The geological history of plants. 204. 
