Northern Piedmont District. 465 
“ marcated. Heracleum lanatum forms in swampy places a pure growth, as do 
also Veratrum viride and Eupatorium purpureum. Heliopsis laevis, Rudbeckia 
laciniata, Commelina virginica, Polygonum sagittatum, Mentha spicata and Ver- 
‚nonia Noveboracensis are usually together in alluvial bottom lands at the mouths 
of streams where the soil is wet (Heliopsis-Rudbeckia- Association). 
2. Forest formations. 
Deciduous-forest Formation. Originally the forest covered most of the 
surface of southeast Pennsylvania. In some places, notably on the Wissahickon 
Creek within the confines of Fairmount Park and in areas on Crum Creek, 
the primeval forest still remains‘.. A study of such preserves shows the 
character of the original forest. The dominant and secondary trees grow on 
precipitous rocks, on declivitous hillsides, on the plateau surfaces left as a 
remnant of a former peneplain, on the creek bottoms of the region, where 
the trees reach their largest size, and on the Delaware River plain down to 
where the forest formation merges with the river marsh plant formation. All 
the areas occupied by the cultivated-plant formations recognized were covered 
by the original forest”). The original forest was a mesophytic one. It probably 
passed through various vicissitudes dependent upon the topographic changes, 
so that the xerophytic forest of the hillside was gradually replaced by a meso- 
phytic forest. The tendency has been in the entire region to the culmination 
of the forest in the mesophytic type. The forest, of great original density, 
may be looked upon as the’ northeastern extension of the forest found de- 
veloped in its highest character in the region drained by the Tennessee River 
and its tributaries and by streams arising in the southern Alleghany Moun- 
tains and flowing eastward into the Atlantic. Arbitrarily, a line drawn from a 
point where the Ohio joins the Mississippi River, east to the Cumberland Moun- 
tains and thence along the Alleghany Mountains to the west branch of the 
Susquehanna River in Pennsylvania, then to the Blue Ridge and along it to 
the Schuylkill River, following the hills on the south side of the Great Valley 
to the Delaware River, represents the northern limit during glacial times of the 
forest which during the Miocene period extend north into the Arctic regions. 
e northeastern extension of the forest of glacial times was much poorer 
in species than the mixed deciduous forest farther south. This was probably 
due to the killing of the less hardy species by the glacial cold. Only those 
species remained in the area mentioned that were hardy. These hardy species, 
1) Fairmount Park, Philadelphia possesses many fine pieces of woodland, where the original 
forest conditions may be studied. OGLESBY PAUL, landscape gardener of the park, has enumera- 
ted in a brochure of 52 pages,. the prineipal trees and estimated their numerical abundance. The 
list comprises as the most abundant trees of the Park the following: Castanen , Liriodendron, 
Fagus, Quercus alba; Q. tinctoria, Q. Prinus, Fraxinus americana, Acer rubrum and Cornus florida 
as a secondary species. — See plate Xla. 
2) Tro EI Eat The Atlantic Forest Region of North America. The Popular Science 
Monthly LXXV: 370—392. Oct. 1909. 
Harshberger, Survey N.-America. 30 
