IO THE AMERICAN NATURALIST. [VoL. XXXIII 
Pinus Virginiana. — More or less abundant in the coniferous 
zone, often forming small forests. Locally quite frequent in 
the tension zone, especially on the clay belt, but only recorded 
from within the deciduous zone, at widely separated localities 
— New Brunswick, Milford, and Riegelsville. 
Pinus echinata. — Most abundant in the tension zone, often 
forming groves of considerable extent. Less abundant in the 
coniferous zone and not recorded from the deciduous zone. 
Chamecyparis thyoides. — Forms the bulk of the vegetation 
in the cedar swamps of the coniferous zone. Rare in the ten- 
sion zone. Locally abundant in certain swamps in the decidu- 
ous zone. 
Ilex opaca. —Common in wet woods in the coniferous zone. 
Less abundant in the tension zone. Reported from but one 
locality in the deciduous zone, at Carpentersville. 
Quercus Phellos.— More or less abundant in the southern 
part of the state, especially in the tension zone, where it occurs 
close to the Triassic border, but has not been recorded from 
the deciduous zone. 
Quercus nigra. — Practically the same range as the last. 
That the distribution of these species is not wholly due to 
climatic conditions is evident. In the case of Chamecyparts 
we have a species which occurs as far north as Massachusetts, 
and as far south as Florida, its occurrence being determined by 
physiographic conditions. 
In considering others of the species we may even eliminate 
these conditions. Quercus Phellos and Q. nigra, for example, 
extend northward in the eastern part of the state as far as 
Perth Amboy, while in the western part they are not known 
north of Trenton. A line drawn between these two places 
defines the northern limit of distribution for these species. 
The topographic features in the immediate vicinity on both 
sides of this imaginary line are the same, and yet they do not 
cross it. The fact which is at once apparent, however, is that 
_ this line is coincident with the line of demarcation between the 
Triassic and Cretaceous formations, and the rational inference 
is that this feature is the important one to be studied. These 
ts two species are taken as special examples in this connection, 
