302 The American Geologist. November, 1894 
and the Coal Measures proper. The former is of limited de- 
velopment and often entirely wanting. The area occupied by 
these formations is roughly circular in form and is located in 
the central part of the lower peninsula. It covers not far 
from 10,000 square miles, including fourteen entire counties 
and parts of as many more. 
Boundary of tup: District. 
The surface is so generally covered with drift that its exact 
limits cannot be readily ascertained. Much of the boundary, 
however, may be located with reasonable accuracy from the 
presence of occasional outcrops. According to Prof. Romiri- 
ger (Geol. Survey of Mich., vol. in, 1876), the boundary is 
about as follows: Commencing at a point on Saginaw bay, 
in the northern part of Huron county; thence southwesterly 
in a gentle curve to the southern part of Jackson county, 
within about 30 miles of the southern state line; thence north- 
west to the vicinity of Grand Rapids, about 25 miles from 
lake Michigan; thence north, northeast and east with a sweep- 
ing curve, to the north shore of Saginaw bay, opposite the 
place of beginning. From Grand Rapids to the vicinity of 
Saginaw bay the location of the boundary is largely guess- 
work, owing to the heavy drift with which the region is cov- 
ered. 
Topography. 
A marked depression crosses the peninsula from Saginaw 
bay to the mouth of Grand river, dividing the Carboniferous 
area into two nearly equal parts. Its direction is southwest 
from Saginaw bay to the mouth of the Maple river, in Ionia 
county, thence west to lake Michigan. According to the late 
Prof. A. Winchell, one may cross the state along this line 
without reaching an altitude greater than 72 feet above the 
lakes. The highest point is in Gratiot county, probably in 
North Star township (T. 10 N., R. 2 W.), where the waters 
flowing into the Bad and Maple rivers separate. The northern 
and southern portions of the district incline gently to the 
central depression. The point where this depression crosses 
the western margin of the Carboniferous area is but a few feet 
above lake Michigan, the site of the union depot in Grand 
Rapids, having an altitude of only 20 feet. The eastern end 
of the depression merges into Saginaw bay. From these two 
