1914J 
Jackson: Land Vertebrates of Ridgeway Bog 
27 
gained a foothold with much greater difficulty. Upon the ele- 
vations alone was there sufficient drainage to permit the develop- 
ment of an early terrestrial vegetation” (Shimek, 1908, p. 59). 
The laminations of humus in the hill bordering Ridgeway Bog 
are not numerous and are nowhere at any great depth beneath the 
surface, which would lead one to conclude that the sand dune 
formation was not long continued and that vegetation soon gained 
a foothold. There is no reason to think that the invasion and 
succession of vegetation which took place on this sand dune area 
was essentially different from similar processes taking place at 
the present time in sand dune areas in the northern sections of 
temperate North America. The plants were not necessarily con- 
specific with the plants reclaiming dune areas in the same region 
today, though in many cases they probably were specifically the 
same; they were, however, ecologically equivalent. The first 
tree growth to invade these dunes after the bush society probably 
consisted of such species as Populus tremuloides, Populus grandi- 
dentata, Betula papyrifera, Pinus divaricata, and associated plants, 
which would be followed by Pinus resmosa and Pinus strohus. 
vSuccession in the Hillside Association has evidently been slow, 
changes few, and the biota as found at present has probably been 
more or less characteristic for a long time. 
The time required for the transformation of a lake into a marsh 
or bog is dependent upon many conditions, such as the physio- 
graphic features of the surrounding country, the depth and size 
of the lake, the slope and contour of the shore and bed of the 
lake, the nature of inflowing and outflowing streams, wind ex- 
posure and associated with it wave action and lake currents, 
plant growth, and deposition of plant and animal remains. The 
original lake which occupied the Ridgeway Bog area had a very 
irregular shore line and was well protected from wind on all sides 
except the north by relatively high hills, though the slopes except 
on the west were not steep; consequently wave and lake current 
action were reduced. The hills bordering the lake were all com- 
posed largely of sand and loose glacial till which was easily eroded 
both by wind and water and deposited into the lake, where the 
weak drainage and frequent irregularities in the shore line pre- 
vented its being carried away. Thus benches and submerged 
flats formed along shore, upon the shallower parts of which the 
Aquatic Association secured foothold. 
