558 J. E. Hyde — Notes on the Absence of a Soil Bed. 



above sea-level, some trace of the subaerial exposure would be 

 visible at the contact. 



The following facts concerning one erosion surface are 

 presented solely as evidence against Willis' interpretation of 

 the significance of the absence of soil beds or other evidence 

 of exposure. The point which it is desired to make is that 

 there may be no evidence of such a period of exposure at a 

 contact which undoubtedly stands for several hundred feet of 

 erosion, apparently under conditions highly favorable for soil 

 formation. The explanation of the absence in this case cannot 

 possibly be the one given by Willis, but no reason is, as yet, 

 to be assigned. 



The base of the Pennsylvanian series, or Coal-measures, 

 along the outcrop belt in central and southern Ohio usually 

 rests directly on the Logan formations whose general age is 

 early Mississippian. The latter were subjected to erosion 

 which removed an unknown thickness and a relief of 200 

 to 300 feet was established before the Coal-measures were 

 accumulated. At several points the Maxville limestone, late 

 Mississippian in age, is found between the two, but it occurs 

 only in patches. There was some erosion of the Waverly 

 prior to the formation of this limestone, but it is very probable 

 from the general field relations that by far the most of the 

 erosion was in post-Maxville time. The irregularity in the 

 distribution of this formation is to be explained, in large part 

 at least, by the attitude of the post-Maxville erosion surface. 



This plane of disconformity extends entirely across Ohio. 

 It has recently been followed in some detail from the center 

 of the state to the Ohio river. In places, it cuts very abruptly 

 into the fine-grained yellow sandstones of the Logan forma- 

 tions, sometimes removing them entirely, and letting in coarse, 

 massive Coal-measure sandstoues, but usually the irregularities 

 are gentle and observations of the contact may be necessary 

 over a mile or more, in order to detect any considerable varia- 

 tion. Differences in elevation of 100 feet are not uncommon, 

 although most of them are less. Finally, it is the rule to find 

 it standing uniformly high over considerable areas — several 

 townships — and tending to be lower in adjacent townships. 

 For example, in eastern Fairfield and southern Licking coun- 

 ties it stands very high, about 300 feet of Logan being present 

 at one point. To the northeastward and southwestward it sinks 

 gradually until the Logan averages 60 or 80 feet and to the 

 southwestward may be wanting entirely. At several points 

 where the coarse Coal-measures sandstones are let into the 

 Logan to a depth of 100 or even 200 feet, they take the form 

 of a long, narrow mass which can be traced sometimes three 

 or four miles, and clearly indicate the presence of a valley 

 on the old Waverlv surface. 



