1922] Peattie,— Coastal Plain Element in Flora of Great Lakes 81 
progress inward we do not find the hollows filled with water; they are 
only moist swales, and the ridges are covered by that peculiar vegeta- 
tion which E. J. Hill has called the * pine barrens of Indiana" and Dr. 
H. C. Cowles has classified as evergreen dunes or dune heath. Both 
the swales and the pine ridges show a less-markedly coastal plain char- 
acter. Further inland still the hollows are nearly as dry as the ridges 
and are distinguished by very few coastal plain plants (chiefly areni- 
colous if any) and more and more frequently by prairie types or by the 
oak barrens which are, for the most part, Alleghenian and Carolinian. 
This spot and a few similar ones along the Great Lakes show all 
that are left of conditions which approximate those which must have 
been prevalent on the margins of Lake Algonquin. Judging from the 
large number of old spits and beach ridges which have been traced out 
for the glacial lakes giving rise to Lake Erie and Lake Michigan, it is 
reasonable to imagine.their shores to have been an intricate series of 
lagoons, ridges, strands and low dunes, harboring the newly-migrated 
coastal plain and strand types. This is the more evident when we see 
that considerable numbers of coastal plain species occur to-day in such 
places, and rarely occur in others. 
FLORA OF THE OUTLETS OF THE GLACIAL LAKES. 
It might reasonably be expected that where there were important 
inlets and outlets of the glacial lakes system, there would be isola- 
tions of coastal plain plants. And this is precisely what we find. 
The narrow St. Clair River, which at the present day forms the connec- 
tive between Lake Huron and Lake Erie, has at all stages been the only 
connection. This then, is the gate through which all coastal plain 
migrations necessarily took place. And it is interesting to record 
that the coastal plain flora of Port Huron and its vicinity, at the out- 
flow of Lake Huron, is large. So also are the floras of Saginaw Bay 
and Grand Rapids, which are, respectively at the east and west extrem- 
ities of the Grand River Valley, the one-time connective across Mich- 
igan, seen in Figure 3. 
The flora of the Hudson-Mohawk Valley and of the Lake Ontario 
basin of New York State, particularly around Oneida Lake, contains 
almost as many coastal plain species as the head of Lake Michigan. 
The area shows, of course, a good many types which come up from the 
Atlantic seaboard and do not extend further inland, but they also, 
with the presence of a large number of the coastal plain types which 
