6 BULLETIN 142, U. S. DEPARTMENT OF AGRICULTURE. 
PHYSICAL FEATURES. 
The soils of the Miami series occur in the northeastern part of 
the great Central Plain, which extends from the region of the 
Great Lakes southward beyond the Ohio River and westward be- 
yond the Mississippi. The greater part of this area, especially 
the extensive tracts in western Ohio and in central Indiana, is 
drained by streams belonging to the Mississippi drainage system. 
Large areas in the northern region are drained by the small tribu- 
taries of the Great Lakes. In general, the region consists mainly 
of extensive plains which range from about 600 feet in altitude to 
extreme elevations of 1,500 feet above sea level. 
The broader features of topographic relief within this region are 
primarily due to the elevation of the rock floor which underlies the 
surface deposits. The eastern border of the region is indistinctly 
separated from the more elevated Appalachian Plateau by a transi- 
tion from the more rugged topography of the plateau to the gently 
undulating plains to the west. Along a large part of this border the 
difference in relief is not so pronounced as to form a distinct bound- 
ary, there being only a gentle gradation from hilly and dissected 
country into a region whose interstream areas are but gently undu- 
lating and within which the major streams occupy narrow or broad 
trenched valleys of no great depth. Along this eastern border the 
elevation of the plain ranges from about 700 feet, east of Chillicothe, 
Ohio, to approximately 900 feet immediately east of Columbus and 
about 1,000 feet to the east of Bucyrus. Near its eastern border 
that part of the plain occupied by the soils of the Miami series sinks 
gently toward the basin of Lake Erie, the northeastern border of 
the section following the ancient shore lines of the glacial lake which 
occupied the Maumee Basin. This shore line has an elevation of 
about 800 feet above tide level throughout its extent, from Tiffin, 
Ohio, to Fort Wayne, Ind. The eastern boundary of the area, ex- 
tending from Fort Wayne to Bad Axe, Mich., has approximately 
the same elevation. 
From the eastern border of this region in central Ohio the plains 
undulate westward, gradually increasing in elevation until a maxi- 
mum altitude of 1,500 feet is attained over a small area in the vicin- 
ity of Belief ontaine. This marks the extreme altitude in an elevated 
ridge which extends in an almost due north and south direction from 
the vicinity of Bellefontaine to that of Hillsboro. This ridge varies 
from 25 to 40 miles in width and has an elevation of more than 1,000 
feet. It constitutes a gently rolling watershed separating the drain- 
age of the Scioto Eiver from that of the Mad River and the Little 
Miami. 
