Devonian Shales of Northern Ohio. 207 



eral relations of the Cleveland shale and the Devonian lime- 

 stone across northern Ohio as regards dip are clearly shown in 

 the chart of sections, figure 2. The well records show an east- 

 ward declination of the Devonian limestone across the north- 

 ern part of the state which varies somewhat in different areas 

 just as the dip of the outcropping Devonian shales, hut con- 

 versely. Thus the easterly dip of the Devonian limestone 

 from Wilmer, near Sandusky, to the Gillman well, \\ miles 

 southeast of Huron, is 31 feet per mile ; from the latter point 

 to Lorain it is about 20 feet per mile. Between Lorain and 

 Cleveland the rate decreases to about 10 feet per mile. From 

 Cleveland to Jefferson near the northeastern border of the 

 state about the same rate of 10 feet per mile is maintained. 



We have for the declination of the base of the Cleveland 

 shale the more precise data derived from surface observation 

 and aneroid measurements of extensive exposures. The most 

 easterly outcrop of the Cleveland shale examined is 2 miles 

 west of East Trumbull, or 20 miles west of the Ohio and Penn- 

 sylvania state boundary. Here the base of the formation lies 

 at about 990 feet above sea-level.* West of this point 11 miles, 

 near Big Creek, the base of the Cleveland lies at nearly the 

 same level, thus showing no dip. From the Big Creek section 

 westward, however, there is a very gentle westerly dip. At 

 Gates Mill, 17 miles west of the Big Creek section, the Cleve- 

 land has dropped to 880 feet, a dip of about 6 feet per mile. 

 From Gates Mill to Rocky River west of Cleveland, a distance 

 of 22 miles, the formation descends 200 feet or 6 feet per mile. 

 A slightly lower rate of 8 feet per mile is maintained west of 

 Rocky River between Dover Bay and the mouth of Porter 

 Creek. West of Rocky River nearly continuous cliffs along 

 the lake front continue with very few and short breaks nearly 

 to Rocky River and afford opportunities for observing struc- 

 tural features along more than 12 miles of lake front unequal- 

 led in northern Ohio. For the first three miles of these cliffs 

 there is no deviation from a uniform westerly dip of about 8 

 feet to the mile, a rate very similar to that prevailing for 40 

 miles east of Rocky River. At Eagle Cliff, however, the per- 

 fectly uniform gentle westerly slant of the strata, so well 

 shown between Dover Bay pier and the mouth of Porter Creek, 

 changes to a succession of low north and south trending anti- 

 clinal rolls. With few exceptions these structures have very 

 low ai-ches, nearly flat on top, which rise above their troughs 

 from 3 to 8 feet. The width of these gentle undulations 

 usually ranges between 200 and 350 yards, giving an effect not 

 nnlike the billowy surface of a subsiding sea. An exception- 



* The figures given here are aneroid measurements checked with the near- 

 est bench marks. 



