590 C. WHITTLESEY ON THE PHYSICAL 



the mean elevation of Lake Erie at 564.13 feet, as given above, the directrix should not 

 vary more than half a foot from five hundred and sixty-six and a half (566$) feet above 

 tide. The elevations below given, refer to this mean water line, unless the city zero is men- 

 tioned ; which mean level is considered as five hundred and sixty-four (564) feet. Fractions 

 of feet will generally be omitted. A third source of error arises from the uncertainty of 

 the zero, or starting point, of some of the interior surveys. This does not exceed the other 

 errors incident to disconnected surveys, made by different persons, at different times, 

 under no official or State supervision. We think the greatest correction cannot exceed 

 plus and minus five ; so that the greatest error will not exceed ten feet, and in nearly all 

 cases will be within three feet. A large part of the figures are correct within half a foot. 



Triangulations for Dip in the Coal Series. 



In Ohio, the coal-bearing rocks are the most recent of the indurated strata, forming a 

 large segment of the great Appalachian coal field. The only newer beds in the State are 

 the Quaternary, or drift, which everywhere cover the indurated rocks. On my geological 

 maps of 1856 and 1869, the coal region occupies about one third of the State, on the east 

 and southeast. From the curved lines of outcrop, where the conglomerate comes up on 

 the north, northwest, and west, the dip of the coal strata is in the opposite direction, south 

 and southeasterly, as the following calculations will show. These and all the Ohio rocks 

 are so nearly level, that the inclination is not in general perceptible to the eye, except in 

 cases of local undulations. Around the base of the coal, the succeeding formations are 

 generally conformable, over a wide field, to the north and west ; but in the southwestern 

 part of the State is a low crown or flat dome, where the silurian strata dip in all directions. 



TaUmculge, Briar Hill, and BrooJcfield. — At the Northwest Six Corners, Tallmadge, Summit 

 County, the lowest coal seam (Newberry's old entry) is 527 feet above Lake Erie; thence 

 to Briar Hill (old entry), near Youngstown, Mahoning County, the course is east 41.2 

 miles, 342 feet above Lake Erie ; thence north 33^° east, 11$ miles, is Curtis' old entry, 

 in Brookfield, on State Line, near Sharon, Pennsylvania, and nearly on the line of bearing. 

 These points fix the direction of the dip, at south 12.$° east ; rate 20.6 feet per mile. 

 " Coal Hill," Tallmadge, is an outlier of the coal series, 1$ miles long, north and south 

 beneath which the coal is mostly worked out. From the north end, at the Northwest Six 

 Corners, to the south end, the bed, which lies in the form of a local basin, sinks 28 feet. 

 The mean of the lowest parts of the mines is 505 feet A, the sump of Newberry's old mine 

 is 517 feet, and that of Briar Hill, 318 feet A. Two mines at the mouth of Newman's 

 Creek, near Massillon, Stark County, the Union Company's sump (346 feet A), the Massillon 

 Company's sump on the same level, combined with Tallmadge and Briar Hill, give for the 

 dip of the bottom seam, south 53$° east, 84 feet per mile. At Massillon, and on Newman's 

 Creek, the local basins have their outcropping edges from twenty to forty feet above the 

 sumps of the mines. Some short lines in the lower seam, around Clinton, Summit County 

 between Massillon and Tallmadge, give for local dip, south 23$° east, 9.1 feet per mile, and 

 in the valley of Newman's Creek, south 71° east, 15.6 feet per mile, disclosing local irreg- 

 ularities such as appear in all parts of the field. The general elevation of these mines 

 will be found below. Around Bolivar, about twelve miles below Massillon, on the Tusca- 

 rawas, the lowest bed of limestone in the coal series, which is about 160 feet above the 

 lowest coal seam, is well developed. By lines from three to five miles in length, in this 



