BIG SPRING PRAIRIE. 69 
without forming a distinct or characteristic sand dune 
as commonly understood. It may have been more 
distinct in the past than at present. Now it may more 
properly be termed a sand slope. 
The characteristic vegetation is quite similar to 
that found on the north slopes of the ridges, the oaks 
and hickories predominating. The grass is chiefly Poa 
compressa. A portion of this sandy slope is under 
cultivation. 
In Big Spring Township, Seneca county, there 
occur three distinct dunes, two of them marked S. D. 
on map I, meaning simple dunes. The one to the 
southwest, illustrated by fig. 14, will be referred to as 
West Dune, the other as North Dune. M. D. C. in- 
dicates a Miniture Dune Complex. 
By inspection of map I, it will be noted that 
these dunes are located between the Bower Ditch on 
the north and the outlet of the Big Spring on the 
south. Asa natural stream, the Bower Ditch had eroded 
a perceptible valley on the ridge to the northeast, and 
had donbtless carried a considerable amount of silt into 
the old lake. The natural currents from the Big Spring 
and those from the south also carry some silt along. 
As these two silt laden currents encountered the sweep 
of the prevailing westerly winds, much of this silt 
was deposited, and in time, formed a sand bar or bank. 
After portions of this sand bar became sufficiently ele- 
vated to remain above the water throughout the year, 
low dunes would be formed by the action of the winds. 
Seeds would soon find lodgment, and plant life appear. 
The same currents which transported the silt, would 
also transport many seeds. The general order of the 
advance of plant life on these dunes would resemble 
that of the sand dunes along Lake Michigan. First, 
there would appear annuals, then grasses and sedges, 
which would act as binders of sand and in consequence 
low dunes would form; after this, shrubs and tree 
