445 
A rather large bay, called Skokie Bay, extended northward for 
a considerable distance. It is this ancient Skokie Bay which, when 
the ice-sheet had retreated to such an extent that Lake Chicago (now 
Lake Michigan) no longer discharged its waters by way of the Des- 
plaines-Illinois rivers, became partly drained and now forms the 
region familiarly known as the Skokie Marsh. A second bay lay 
to the west of Skokie Bay. A glance at the cross-section on the 
map (Fig. 1) will show the relation of Skokie Bay to this small bay, 
the Glenwood ridge separating the two. It seems evident, that ata 
stage later than the time at which the Glenwood ridge was formed, 
there must have been a period when Skokie Bay was itself divided 
into two arms. This condition is very plainly marked in the 
topography of the country, the ridge between the east and west shores 
of Skokie Bay being one of the conspicuous features of the land- 
scape, especially at its highest point, overlooking the East Branch of 
the Chicago River. This ridge attains an elevation of twenty feet 
above the surface of the stream. The height of the Glenwood ridge 
in this area is 670 feet, or twenty feet above the ridge previously 
mentioned. The cross-section shows the relation of these three 
elevations. The view of the Skokie Marsh from the top of the 
highest ridge at the western edge of the town of Glencoe, is really 
quite picturesque, and on a bright, cool morning in early spring is 
sure to leave a lasting and pleasing impression. 
The recession of the water of Skokie Bay has left some peculiar 
topographic features: the bed of the bay proper (see map and 
section) is now the Skokie Marsh; the surface of the ridge, which 
divided Skokie Bay into two arms and which was probably a long 
sand spit, contains a large number of pools of various sizes, which 
are more or less dry in the summer and fall; this area is rather 
sparsely wooded; the smaller arm of Skokie Bay is now occupied by 
the East Branch of the North Branch of the Chicago River; the 
small bay to the west of Skokie Bay is now occupied by the North 
Branch of the Chicago River, while the ridge between these two 
streams, which is believed to be equivalent to the Glenwood beach, 
is heavily wooded, with but few of the small pools so characteristic 
of the lower ridge to the east. 
The area surveyed, which is three miles long and one mile wide, 
is thus seen to comprise five rather distinct areas, which may be 
designated as A, B, C, D and E. 
