THE LOWER COAL MEASURES. 139 
cases directly south. A westerly element comes in if we advance to 
the southeast into Pennsylvania, but as we pass to the westward through 
the Ohio Coal Measure counties, an easterly element of the dip is soon 
recognized. ‘This element gradually increases, until on the western 
boundary of the field it often predominates over the southerly direc- 
tion, and sometimes completely extinguishes it. The dip of the Ohio 
Coal Measures is thus seen to range from south or nearly south upon 
the northern boundary of the field, to east or nearly east on the extreme 
western boundary, and its predominant direction is southeasterly. For 
considerable areas, the dip often proves quite constant, and here it is pos- 
sible to determine the elevation of a coal seam, for example, in some 
locality where it has not been opened, by calculations based on the dip 
of the seam, established on its known elevations in the vicinity. It is 
never safe, however, to trust absolutely to this method of determining 
the stratigraphical relations of a varied series, for the direction and 
amount of the dip are often found to change enough in short compass 
to vitiate any nice determinations founded upon them. 
The same inclination in direction and amount is shared by the 
formations that underlie the Coal Measures in the Ohio basin. ‘This 
has already been stated, at least by implication, in the earlier pages of 
the chapter. Not only the Berea Grit and the other divisions of the 
Sub-carboniferous age, but the Devonian and Upper Silurian formations 
of Central and Southwestern Ohio as well are all characterized by this 
monotonous southeasterly dip. ‘The steady elevation of the Cincinnati 
Axis seems adequate to account for it, the dip being at right angles to 
the general direction of this line of elevation. 
Reference has already been made to the fact that the Coal Measures 
of Ohio are traversed by occasional folds, low in elevation and gentle 
in pitch. Their direction is in the main the same as that of the Cin- 
einnati Axis and the Appalachian Mountain system, viz., northeast and 
southwest. They are generally referred to the time of the great 
disturbances that followed the Carboniferous age, and which raised so 
conspicuous a portion of the eastern border of the continent. These 
folds of necessity reverse or intensify the prevailing dip in their imme- 
- diate vicinity, but they are after all folds in a series already inclined, 
and they scarcely break in upon the regularity of this inclination in the 
large way. The reversed dips which Newberry finds in the Tuscarawas 
valley and elsewhere are in many cases to be referred to the duplication 
