Drainage of Carboniferous Area, Michigan. — Mudge. 303 
low-lying points the boundary rises in each direction. The 
northern rim attains an altitude of about 500 feet, reaching 
well up toward the high northern plateau. The elevation of 
the southern margin is perhaps a little greater. 
The Drainage Systems. 
An inspection of a geological map reveals at once an inti- 
mate coincidence between the drainage areas of the district 
and the limits of the district itself. The boundary as above 
described, except where it crosses the central depression, 
marks, approxiniatety, the watershed between the streams 
draining the district and those flowing in various outward di- 
rections. This peculiarity is more particularly noticeable 
along the southern margin of the territory. From the vicinity 
of Grand river on the west, to Howell on the east, a distance 
of about 150 miles, the coincidence is nearly continuous, the 
only notable exception being in Calhoun county, where the 
northern branches of the Kalamazoo, rising some distance 
within the district, flow outwardly across the border. From 
Howell northeast to Saginaw bay, the boundary is some dis- 
tance west of the watershed, the eastern members of the Sagi- 
naw river system rising outside the district and flowing in- 
wardly. On the northwestern border for a distance of seven- 
ty-five miles, the Muskegon river is within the boundary and 
only a few miles from it, thus apparently contradicting the 
rule laid down above. Nevertheless the rule is in some de- 
gree applicable, as will be seen later on. 
There are two principal river systems in the district, the 
Grand and the Saginaw, which carry off nearly all the water 
falling within it, and but very little from outside territory. 
The line of separation between them runs from the margin of 
the district in Livingston county in a general northwest di- 
rection to Mecosta county. The territory drained by each is 
broad and irregular in shape, while nearly every other stream 
of importance within the state occupies a more or less elongated 
valley. The only remaining river worthy of mention within 
the district is the .Muskegon, which drains a narrow strip on 
the northwestern margin. 
Genesis of the River Systems. 
That the history of all the streams in this region dates 
from the close of the Glacial period is quite apparent. For 
