118 ILLINOIS ACADEMY OF SCIENCE 
are conspicuous. The other sides are being eroded but show 
signs of having been covered with forest. 
It seems quite probable that dunes of the size of Sleeping 
Bear or even larger could have been formed at the top of a high 
shore cliff, but it is difficult to imagine that the great mass of 
sand that has been swept from the morainic plateau and forms 
the great moving dune advancing towards the east could have 
been so brought up from the lake at least 300 feet below. The 
hypothesis of a terrestrial origin for the sand would on the 
contrary seem more suited to explain the situation if it could 
be supported by adequate data. Such data have not been ob- 
tained in the Sleeping Bear area but appear upon one of the 
islands to the north. 
- South Fox Island, lying in Lake Michigan about 35 miles 
north of Sleeping Bear Point is about 5 miles long and a fourth 
as wide, the long axis of the island running some 30° west of 
north. The chief topographical features are a continuous 
ridge of morainic material capped with dunes, varying from 
200 to 325 feet in height, and from 200 to 400 yards in width, 
running along the western side and a gravelly plain of low 
elevation which occupies. the eastern side of the island 
(Fig. 4A). 
The western shore is being rapidly eroded and the cliffs rise 
abruptly from a very narrow beach strewn with pebbles and 
glacial boulders. The cliffs are composed of mixed morainic 
clays and gravels while a distinct horizontal line separates the 
lower more stony mass from the upper more sandy material. 
This line has an elevation running from about 125 feet at the 
south of the island to somewhat more than 200 feet at the 
north. This upper stratum of sandy material has been some- 
what worked over by the wind and at least one large wind 
sweep has developed, the trough being floored with glacial 
gravel and the whole terminating in a bald dune, about 525 feet 
high, forming the highest elevation upon the island (Fig. 4B). 
Much of the sandy stratum, however, presents evidence of hav- 
ing been deposited by agencies other than wind. The evidence 
consists in an admixture of pebbles, bits of rock, and particles 
of soil both larger and smaller than the grains of wind-blown 
