UPLIFT FOLLOWING THE BEDFORD 211 



vailed over the channeled district, while marine conditions were brought 

 about in western Pennsylvania. 



Importance of the Unconfokmity 



Unlike many imconformities in horizontal rocks, that between the Bed- 

 ford and Berea is exceedingly plain. Evidence for it fails in few good 

 sections. But how much of a time gap is indicated by it? 



The answer to this question is somewhat affected by two considerations, 

 for which there is little obtainable evidence one way or the other. Had 

 the underlying rocks become indurated during the interval between their 

 deposition and the beginning of Berea time, and if so how thoroughly ? 

 Did perhaps a long time gap intervene between the close of the Bedford 

 and the beginning of the Berea, a time during which the land lay quiet 

 at low altitude, experiencing neither erosion nor deposit? 



Even with the present degree of induration the rocks which underlie 

 the Berea across Ohio are for the most part so weak that they afford little 

 resistance to currents of even weak erosive power. Many of the shale 

 banks along the stream courses even show rain-gulleying. This is espe- 

 cially true in the western district where the prominent channels occur. 

 They are chiefly cut out in soft red and blue shales, which are even less 

 resistant than a heavy clay soil would be, since they crumble on exposure. 

 The black shales beneath, those in which the bottoms of the deep chan- 

 nels are cut, are not greatly more resistant. They are weak rocks today. 

 The occasional thin sandstones which are cut out present a greater ob- 

 stacle on the supposition that they had so quickly attained their present 

 degree of induration, and it is on their evidence that Prosser chiefly bases 

 his conception of the importance of the unconformity. But if the time 

 gap was small, as we conceive it, it is certainly not illogical to hold tliat 

 it is unlikely that these sands had so quickly attained their present com- 

 [)actness. Tlie quotations from Newberry, with which this paper begins, 

 shows this to have been his view. When one considers the general condi- 

 tion ill wliicli many rocks of Tertiary age are found today, in districts 

 unaffected by orogenic or igiieous activity, the supposition seems not 

 unreasonable. But we may grant that the rocks had attained their pii-s- 

 ent <legree of indiii'at ion lid'occ Borca deposition began and yet not ma- 

 terially alTect our argument. We regard it as prol)at)le that induration 

 was not far advanced, because all other features of the break speak for a 

 very short time gaj). Jiut tlie present degree of indnration may be ad- 

 mitted and still not materially affect the force of llie argument. 



The minoi' cliannclin" in the eastern region is likelv the result of scour 



