10 HARPER: EXPLORATIONS IN THE COASTAL PLAIN 4 
problem of determining the exact location of the fall-line, or inland | 
boundary of the coastal plain. I ascended the Savannah, Ocmul- 
gee, Flint and Chattahoochee Rivers and Rocky Comfort Creek 
(the latter in Glascock County) to beyond their intersections with ] 
this line, and also followed it pretty closely by rail through the ~ 
counties of Muscogee and Talbot. | : 
Many of the oldest and largest cities of the Middle and South 
Atlantic States are situated on this fall-line, which usually marks 
the head of navigation, and in many cases the greatest water- — 
power, on the rivers which cross it. But botanists who have col-_ 
lected around these cities have almost invariably failed to indicate | 
whether their plants came from the hill country above or the 4 
coastal plain below. From a phytogeographical standpoint this — 
is a Most serious omission, for the fall-line, throughout its length — 
of hundreds of miles, is (in the words of Dr. McGee *) “ one of the 
most strongly marked physiographic and cultural lines on the — 
surface of the globe,’”’ and “the most important structural line of — 
eastern United States.’’ The rather vaguely defined “ Austrori-— 
parian area’’ of some botanists — or rather biologists — is prac- 
tically the coastal plain, and the boundary between that and the > 
*Carolinian area”’ is simply the fall-line, the cause of which is 
purely geological, and not climatic. 
It should not be inferred, however, that the fall-line is always 
so sharply defined as to be visible in the field at a single glance. 
On the contrary it cannot usually be definitely located within a_ 
mile or two, except along the larger streams. Nevertheless, it 
seems to be an impassable barrier for many species of plants ; and _ 
the great difference in aspect of the topography and flora on 
opposite sides of this line is apparent to the most indifferent — 
observer. 3 
A few places of historical or geographical interest visited on — 
this trip will now be mentioned. 
In June I spent a week in the vicinity of Augusta, where the — 
most interesting natural feature, to a botanist at least, is the sand- : 
hills, so well known to winter visitors. These are part of a line 
of sandy elevations which extend along or near the fall-line from 
* Ann. Rep. U. S. Geol. Surv. 12!: 356, 357. 1891. The introductory portion 
of this paper is recommended to the careful consideration of the reader. : 
