HARPER: PLANT POPULATION OF MICHIGAN 25 
consideration these are exposed only in limited areas near the 
Great Lakes, and have little influence on soil or topography. The 
interior is covered by glacial drift, averaging several hundred feet 
thick and composed of sand, clay, pebbles and small boulders in 
various proportions. The pebbles and boulders are quite diverse 
lithologically, but most of them are more or less calcareous. Few 
of the boulders are more than a foot or two in diameter, or large 
enough to support any characteristic vegetation. 
There is only one government soil survey for this region as yet, 
and that is for one of the counties at its southern edge. But 
Leverett’s bulletin, above cited, divides the soils of the Lower 
Peninsula into about half a dozen classes, and gives the approxi- 
mate acreage of each in every township and county. From the 
returns from the twenty-one northernmost counties the following 
percentages have been computed; and the corresponding figures 
for the remaining forty-seven counties are given in an adjacent 
column for purposes of comparison. 
Northern Central and 
Soil classes counties southern counties 
OGY CU oo as Pal ke va eee a 26.9 21.0 
oo ee ers rater cep aes a ee 25.9 24.7 
CAVey Ss oer ess SC a a eek 18.6 38.2 
Swarine and lakeee os eee et 17.9 8.8 
CHavely IOAN oe. os ee ee ea 9.7 6.7 
CHAVGE Se oo ori eae Ct i ee ee 1.0 0.5 
The clayey till includes both moraines and glacial-lake de- 
posits, which could have been separated if it had seemed worth 
while. (The latter type in Michigan is chiefly confined to the 
vicinity of Saginaw Bay and Lake Erie, and is very sparingly 
represented in the region under consideration). Some of the larger 
interior lakes are excluded from the estimate for swamps and lakes. 
The sand on many of the uplands is so deep and loose as to 
make walking and hauling on unimproved roads somewhat diffi- 
cult in dry weather, just as in many parts of Florida. No satis- 
factory chemical analyses of the soils seem to be available, but 
they are doubtless below the average in fertility. 
Topography and hydrography.—The topography is that com- 
mon to many glaciated regions, undulating to hilly, with numerous 
depressions containing lakes, ponds, swamps, bogs, marshes, etc. 
The largest lakes cover about thirty-five square miles. The highest 
