136 Geology of Upper Illinois. 
road for about fifteen miles is on the beach, or just behind it, on 
the border of the level prairie. It then begins to diverge from 
the shore, and passes obliquely across a succession of ridges, each 
resembling a turnpike in its rounded form. These ridges are 
wooded, while the intervals between them consist of wet marsh, 
or level prairie. Advantage is taken of the ridges as far as pos- 
sible for the course of the road. After proceeding a number of 
miles in a south-easterly direction, the road takes a south course 
at right angles to the coast, and runs for a distance of five miles’ 
over about fifty of these ridges. They vary from four to ten rods 
in width, each one, however, preserving with exact uniformity 
its own breadth, and separated from each other by intervals of 
from six to forty rods. When midway between any two beaches, 
the eye is presented in opposite directions with an almost inter- 
minable vista, whose bounding lines of trees are perceived to be 
slightly curvilinear, the curvature of the ridges corresponding ex- 
actly to the broad sweep of the lake shore. No sensible differ- 
ence of level is apparent in the beaches, while the marshy prairie 
between them is so low and sunken as to be almost impassable, 
and apparently corresponds in level with the prairie in rear of 
Chicago. 
At the termination of the above series, commences a new order 
of ridges, all of which are situated at a somewhat higher level. 
They have an average width of only one hundred and twenty 
feet, and. are Besepersied by depressions of the same dimensions. 
In these, both the ridge and the valley are dry and wooded. 
The road crosses them for the distance of one mile, after which, 
assuming a more easterly cousre, it descends upon a flat prairie, 
about three miles wide, from which it rises over a wooded swell 
of land half a mile wide, and again comes upon a broad expanse 
of wet prairie. It afterwards turns still more to the east, and 
continues over high rolling land to Michigan city. As the last 
fifteen miles of the ride was by night, I cannot record the remain- 
ing features of the route. 
The succession of beaches described, would appear to have 
been occasioned by the action of northerly winds operating on 
the whole range of the lake, thereby producing an accumulation 
of water in this region, as well as a strong impulsive action upon 
the bottom of the lake from the motion of the sea towards the 
shore. - Be. ae ae ec cece eta 
