72 Cincinnati Society of Natural History. 



thickness; that after the Carboniferous Era occurred the great 

 Appalachian upHft (the fault along that line seldom being estimated 

 at less than twenty thousand feet, of which at least three miles in 

 depth has weathered away), we must inevitably conclude that the 

 Silurian Seas, in which these rocks were deposited, existed at a 

 time so remote that the years that have passed would be expressed 

 by a number to us utterly incomprehensible — we rather agree with 

 Hutton that "There are no traces of a beginning, no prospect of 

 an end." 



After this limestone plateau had withstood the weathering action 

 of the countless ages required for the formation of the Devonian 

 rocks, and had contributed of its substance for that purpose ; 

 after it had sent its timber rafts both East and West to aid in 

 forming the great coal deposits of America (and after the coal had 

 been covered by the Lias, the Oolitic, the Cretaceous and the 

 Tertiary formations), came that peculiar period commonly known 

 as "the Glacial Epoch," when this area received its first addition 

 from the surrounding country since the time it first emerged from 

 the Silurian Seas. The hills and vales that we now see came 

 forth in substantially their present form from the fearful ordeal of 

 that indefinable and debatable epoch. 



Although among the most recent of geological formations, and 

 exposed to the direct examination of all who care to study its pecu- 

 liarities, and although it is of the greatest utility to man, yet the 

 study of "The Drift" has given rise to greater diversity of opinions 

 among geological students than any or all other formations com- 

 bined. From the weird, fascinating theory of Ignatius Donnelly, 

 who advances the idea that our planet collided with a comet and 

 was covered with dust from its tail, to the skeptical assertion of a 

 Miller, who claims that no such epoch ever occurred, we have sur- 

 mises and theories sufficient to cover all intermediate ground. 



Whatever may have been the condition or climate of this planet 

 during this epoch, or whether or not there occurred an interglacial 

 epoch of ten thousand five hundred years as evidenced by the 

 precession of the equinoxes, yet this we know : the sedimentary 

 rocks of the northern portion of the United States are quite gen- 

 erally covered with a clay containing angular fragments and boul- 

 ders of erratic rocks. We call this substance the Boulder Clay, or 

 " Drift. ' We find plateaus or plains grooved by valleys of erosion 

 that are in no way proportioned to the streams that now occupy 

 them. We further find these valleys flanked by, or containing, 



