MERCER COUNTY. — | All 
SURFACE FEATURES AND SOIL. 
The surface of the whole county is a continuous plain, and the changes 
of level in general are due to the inclination of the rocky floor beneath. 
Gentle undulations and local changes of level are, however, due to the 
condition of the Drift deposit. In no county in north-western Ohio has 
that dependence been seen more perfectly exemplified. The whole 
county is underlain by the same member of the Silurian age, except a 
small area in the north-eastern corner, which does not offer such differ- 
ences of character as to permit unequal erosion by the great glacier. Yet 
there may be seen crossing the county three successive ridges, or belts of 
thickening of the Drift deposit, which rise from ten to twenty-five or 
thirty feet above the general level. The location and character of these 
ridges have been sufficiently discussed in foregoing chapters. It is only 
necessary to say at this place that they are believed to be glacial mo- 
raines, marking periodical resting-places in the retreat of the glacier, 
which was prolonged south-westward from the great St. Lawrence valley. 
In crossing these ridges in a southerly direction the face of the country 
is seen to change, not uniformly, but by successive stages, marked by 
the location of the ridges. That part of the county north of the St. 
Mary’s Ridge is flat, and has a close, often damp, clay soil. That portion 
between the Wabash and the St. Mary’s Ridges is also flat, but is char- 
acterized by several prairie tracts. It shows very rarely any gravel in 
the soil or stones on the surface. It is also, strictly, a portion of the 
Black Swamp, and has all its features. Between the Wabash and the 
_ St. John’s Ridges the surface has a very noticeably rolling contour, al- 
though with some flats. The soil is sometimes gravelly. The color of 
. the clay is somewhat lighter, and in general it is more easily subjected 
to perfect artificial drainage. That portion of the county south of the 
St. John’s Ridge is still more gravelly and rolling. 
GEOLOGICAL STRUCTURE: 
The only rock seen in outcrop within the limits of Mercer county be- 
longs to the Guelph phase of the Niagara. These exposures, however, 
extend over the entire length of the county from north to south, and 
there can be but little doubt that that rock underlies the greater part of 
the county. It has not been seen in the eastern portion. Near Fort Re- 
covery, section 19, it is slightly worked and burned for quicklime by 
Thomas Atkinson. It is taken from the bed of the Wabash. It is por- 
ous and fossiliferous, in beds of three to six inches. It is generally of a 
light blue color, with spots of a darker blue, weathering buff or white. 
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