10G The American Geologist. Fi-i». isoi 
and Michigan would by no means diminish the importance of this 
correlation. 
The dips and strikes of paleozoic strata in the northwestern 
corner of Ohio are so strongly conformable to the topography of 
the Trenton area in this region, and erosion has produced at the 
present day such a flattened topograph}', that projections of the 
outcrops of paleozoic strata are almost available for contour lines 
on the contour map of the Trenton strata as published by Prof. 
Orton. Thus the base of the Huron shale at its outcrops corres- 
ponds to the 1000-foot contour line on Prof. Orton's map. The 
base of the Corniferous limestone corresponds to the 750-foot 
contour. The base of the Waterlime agrees in a rough way with 
the 500-foot contour, finding its best expression along the axis of 
the Findlay fold, to be mentioned again later. The discrepancies 
are due chiefly to the more horizontal disposition of the strata 
along the flatter regions of the Cincinnati anticlinal, so that irreg- 
ular erosion in these flat areas produces stronger impressions on 
the geologically colored map. than would be the case if the strata 
had been more inclined, as they are on the Findlay fold. 
Outcrops of strata exposed between western lake Erie and the 
Ohio river along Adams county show similar correlations. Thus 
the base of the Waverly corresponds to the 1000-foot contour of 
Prof. Orton's map. The base of the Corniferous limestone, and 
where the Corniferous is absent, the base of the Huron shale, cor- 
responds with the 750 Coot contour. Again, the base of the 
Waterlime corresponds in a rough way to the 500-foot contour, 
this finding its best expression where nearest the Bucyrus fold, 
towards the Ohio river. 
Where the base of the Waterlime outcrops follows a course 
more removed from the Findlay fold in the north, and from the 
Bucyrus fold on the south, it might be considered to correspond 
rather to the 250-foot contour. The base of the»l|pper Silurian ex- 
posures, however, corresponds quite closely with the zero or tide 
level contour on Prof. Orton's map. It must be remembered that 
this map gives the contours for the Trenton formations of Ohio, not 
of Cincinnati Group rocks, which of course show higher levels. 
If these studies be continued it will also be found that palaeo- 
zoic strata in western Ohio are more highly inclined and show 
narrower limits of outcrops there where also the Trenton topogra- 
