2 THE AMERICAN NATURALIST.  [Vou. XXXIII. 
tions. They appear to depend upon soil characteristics, either 
mechanical or chemical, and these characteristics constitute 
what may be termed the geologic factor, for the reason that 
the nature of the soil in any locality is directly dependent upon 
the nature of the geologic formation in that locality. It is 
with this phase of the subject that this paper is specially 
concerned. 
It is unfortunate that by far the greater number of areal 
investigations which have been undertaken have been restricted 
by artificial boundaries, generally political, such as state or 
country lines, instead of having been extended to their natural 
limits, either physiographic or geologic, and many interesting 
problems, for this reason, have been only partially solved or 
outlined. 
In New Jersey two distinctly defined forest zones have long 
been recognized,! vz., a deciduous and a coniferous — the 
contrast between the two being so obvious as to attract the 
attention of even a superficial observer. On first sight the 
fact that the former zone is roughly confined to the northern 
part of the state, and the latter one to the southern part, might 
seem to indicate that the limits of the zones were determined 
by purely climatic conditions. If, however, the line of demar- 
cation between them be followed across the state, or, better yet, 
beyond the confines of the state, it will at once be apparent 
that it does not coincide with any parallel of latitude or with 
any isothermal line, and also that it is not entirely dependent 
on topography or the physiographic conditions. 
If, however, a geological map of the region be examined, the 
line of demarcation between the two zones will be seen to par- 
allel very closely the general trend of the geologic formations, 
whose outcrops extend in a northeast and southwest direction 
across the state and southward beyond; and the inference is 
natural that this coincidence is not accidental, and that the rea- 
sons for it must be taken into account in studying the problem 
of the limitations of the zones. 
1 For a brief discussion of the subject, see Dr. N. L. Britton’s Catalogue of 
Plants found in New Jersey, introductory chapter, Final Report State Geologist, 
vol. ii (1889), pt. i. 
