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 beacheSj 

 the eye is presented in opposite directions with an almost inter- 

 minable vista, whose bounding hues 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 separated 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. In explanation of the existence of but a single beach- 



