AREA OF STUDY 49 
chiefly between 581 and 600 feet, and presents very little relief. The 
lowest point of land on our map is in the valley of the Illinois River 
below the entrance of the Kankakee. This is 480 feet above tide, or 
tor feet below the level of Lake Michigan. In passing from the lowest 
point in the lake shown on our map to the vicinity of Lake Zurich, which 
is the location of one of the high points on the moraine, one would 
travel 64 miles and make an ascent of only 12 feet per mile on the 
average. Indeed, if Lake Michigan were to become dry and its bottom 
a prairie, it would appear an undulating plain. 
V. CLIMATE AND VEGETATION OF THE AREA 
I. METEOROLOGICAL CONDITIONS AFFECTING ANIMALS (68) 
The table (1) illustrates the fact that there are some notable differ- 
ences between the different parts of our area. Extreme points would 
TABLE I 
RATIO OF 
TEMPERATURE MEAN RAINFALL SUNSHINE RAINFALL TO 
EVAPORATION 
STATION peu to oeeptembet | Year Jul 
__| April April Bereta 
ie | = : to as Year | to pa Year rae 
ean oO ean o tember tember (4 
Mean ptf te of Mean 1888 
Chicago. ..| 62.6 | 70.0 | 55.6 | a8 | 19.3 | 33-4 | 1695 | 2616 05% 
hrs. | hrs, 
South Bend] 65.3 | 76.3 | 54.3 | 49 18.3.) geese | sere emesletoson 
show greater differences. ‘The evaporating power of the air is probably 
one of the best indices of conditions which affect animals. The ratio of 
rainfall to evaporation is the only expression of the evaporating power 
of the air which has been mapped. Fig. 7 shows this phenomenon in 
Central North America, with our area indicated. 
2.. VEGETATION (69, 70) 
Those features of the vegetation which are called climatic must be 
discussed first. The two main climatic divisions of vegetation represented 
in the Chicago area are savanna including the prairie vegetation, and 
deciduous forest. The prairie, or savanna, as distinguished from steppe, 
is a strip of country (the forest-border area) a few hundred miles wide, 
from Athabaska to Texas, where trees, chiefly oak, hickory, basswood, 
