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J04 GEOLOGY OF OHIO. 
tween the Ohio River and Lake Erie, or near the sources of the streams 
which flow in opposite directions from its summit, is a feature in the 
general physiography of north-western Ohio which deserves special men- 
tion. There seems no doubt that they were once shallow lakes. The 
occurrence of shell-marl below the peaty surface, and of sandy deposits 
about their margins, indicates not only that there was a time when they 
were receiving the annual freshet washings of calcareous matter from 
the adjacent Drift surface, but were also agitated by the wind into little 
waves which broke upon a sandy beach. Other similar undrained places 
in the old Drift surface, situated further down the slopes of the great 
watershed, were sooner filled by the greater accumulation of alluvium, 
or were drained by the more rapid excavation of their outlets by the in- 
creased volumes of the streams. There is reason to believe that the ex- 
tensive prairies of Marion and Wyandot counties are analogous to the 
marshes of Hardin county, but were sooner brought into an arable state 
through the action of the Sandusky and the Tymochtee Creek. 
GEOLOGICAL STRUCTURE. 
The old Drift surface has been so little disturbed that the underlying 
rock is very rarely exposed. Hence the details of the geological struc- 
ture are unknown. The boundaries of the formations are drawn in ac- 
. cordance with such outcrops as actually occur, but governed, in the ab-— 
sence of positive knowledge, by the indications of the surface features. 
The Niagara limestone is known to underlie portions of Blanchard, 
Jackson, Pleasant, and Goshen townships, and is also believed to occur 
in Roundhead township, west of the Scioto River. Thus Hardin county 
not only occupies the watershed between Lake Erie and the Ohio River, 
but aiso holds the separating ground between that belt of Niagara area 
which stretches northward to Lake Erie, and that larger area of the same 
great formation which extends south to the Ohio River and west into 
Indiana. What influence this formation may have exerted in locating 
the divide between the two great valleys can only be conjectured. Con- 
sidering, however, its thickness—stated by Prof. Orton to be two hundred 
and seventy-five feet—and its great persistency in withstanding the 
forces of degradation, it certainly could not have been small. 
In Goshen township it is exposed in the bed of Paw Paw Creek, 8. H. $ 
section 36, where it has been a little worked for quicklime, on the land 
of Mr. Stephen Otis; also, on section 5, north, land of Hezekiah Hemp, 
worked for quicklime. 
In Jackson township it has been slightly opened near the Cranberry 
Marsh, on the land of J. P. Pence, N. E. 4 seetion 380. 
