170 
At the beginning of the long glacial period in the Pleistocene 
Epoch, the outlines of South Jersey and its elevation above sea 
level were probably very much like they are today. The ice did 
not reach South Jersey, for the terminal moraine extended from 
Perth Amboy, northwest over the Watchungs at Summit and 
westward to the Delaware at Belvidere. Some glacial material 
was carried down the southward trending valleys of the Rari- 
tan and Musconetcong, but it affected the composition of the 
soils of the Pine Barrens very little. It would not have changed 
them much, anyway, for the source of glacial material was the 
same as that of the detritus of the earlier stream erosion. 
Of the mineral matter carried off the highlands into the 
ocean, or its arms as they may have existed from time to time 
in South Jersey, the quartz was the most resistant, and it makes 
up ninety per cent or more of the material of the Barrens today. 
The softer feldspar tended to break down into muds and clays. 
The magnetite was dissolved by vegetable acids and trans- 
formed into bog iron ore or clay iron stones. The other minerals 
left little trace. The Barrens therefore, when modern plants took 
possession of them in the Cretaceous Period, had a highly sili- 
cious soil, on which humus was slow in forming, except along 
the streams where more sustained moisture and plant decay 
provided narrow strips for a richer flora. Fires were probably 
frequent in the forests established thereon, from lightning, and 
have repeatedly burned over the area from long before the white 
man or the red man, although the former added much to the 
fire hazards, and still does so. 
The advance of the ice in the Pleistocene may not have 
caused so much change in the flora of the Pine Barrens as might 
be imagined. The ice was approaching a line at which the 
warmth of the more southern latitudes balanced the cold which 
caused it, and this balance wavered, as shown by frequent re- 
treats, some small, some great. The Barrens were thirty to sev- 
enty miles south of the greatest advance, and it is quite possible 
that most of the species held their ground. Some species which 
are usually regarded as northern ones driven south before the 
ice, like the Bearberry and Broom Crowberry probably mi- 
grated into the region at that time and one of the most inter- 
esting facts about the flora is that they still remain here. 
After the white man came there was considerable disturb- 
