XV 
Horizon 5, just above the peat, marks the upper or later limit of the 
Mastodon. It was on this soil about six years ago that the bones of a Mastodon 
were found in Chicago, on the south side of Wicker Park near Milwaukee Avenue. 
They were covered with thirteen feet of silt, or as Dr. Andrews suggests, Loess. 
The bones consisting of part of a jaw, teeth, and parts of a few other bones, are 
now in the collection of the Chicago Academy. There is in the Museum of the 
College of Liberal Arts of the Northwestern University a fragment of fossil ivory 
received from the late James L. Milner, afterward connected with the U. S. Fish 
Commission, taken from a gravel pit excavated in the Middle beach in Evanston 
when the Milwaukee Branch of the C. & N. W. B. E. was constructed. From 
what level it was taken, is not now known. The pit appears to have been exca- 
vated to the clay, and the fossil was probably on the same stratum as that at 
Chicago. 
There is no positive evidence that the waters of the lake were salt water at 
the time the Upper beach was deposited. No shells have been found in the beach 
by which the character of the waters could be determined, but the presence of 
sea shore plants now upon the lake shore, and the existence of the marine Mysis 
in the waters of the lake, indicate that at sometime, salt water has existed where 
Lake Michigan now is. The old bay of the lake whose margins are marked by 
the Upper beach, left some silts on its bottom, and in these silts have been 
found fresh water unios. We have fragments of such shells taken from the silts 
at the corner of West Monroe and Morgan Streets in Chicago. 
Between the Middle and Upper beaches in Evanston, is what is known as 
the “Wet” prairie. It lies about fourteen feet above the lake. Its surface is 
nearly a water level. It is two miles wide and ten miles long. The clay is just 
beneath the surface under the whole area, and before it was drained, it was cov- 
ered with water during the wet portion of the year. Southeast of Chicago where 
the ridges are multiplied, the spaces between these ridges are narrow and cov- 
ered with marshes and small ponds. 
Though Cook County, Illinois, and Lake County, Indiana, have neither moun- 
tains nor valleys, no frowning cliffs nor rocky glens, they have an interesting geo- 
logical history, the outcome of which is a very unique botanical area. The rolling 
prairies, the river bottoms, the sandy ridges, the lake shore, the drift clay and 
its ravines, the sloughs among the ridges at the south end of the lake, the 
peat bogs which are found in many places, the shallow ponds and sluggish 
streams, give a great variety of soil for native plants. 
FOREST TREES. 
The forest trees of our district are of great interest in illustrating the ability 
of prairies to support forest growths, as they contain a large variety of forms, 
many of which are widely distributed over North America. 
The area embraced in this Catalogue is included in the fourth division of the 
Atlantic Eegion of forest trees, known as the “Deciduous Forests of the Missis- 
sippi Basin and the Atlantic Plain” (Sargent), for with few exceptions our trees 
are composed of deciduous species. 
In the forest area specimens are found of nearly all the trees growing in the 
State, the wood, according to the Ninth Census Beport, averaging from two to 
