INTRODUCTION. 9 



or along them are features of a reversed drainage, of pre-glacial 

 age, toward the northwest; and that it is the latter which has 

 been again reversed and sent ofi. to the southwest by the con- 

 tinental ice-sheet. 



A serious objection, and one which may be fatal to this sug- 

 gestion, is the great length of time that has elapsed since the Ap- 

 palachians were formed. This is sufficient for subsequent erosion 

 to have efifaced all inequalities of level which prevailed in the 

 central valleys at that period. However, minor oscillitations may 

 have occurred which would preserve or perpetuate the older 

 valleys. 



At any rate, whether any evidence now remains of it or not, 

 there must have been a form.er drainage from western Ohio to- 

 ward the eastward ; and this drainage must have become reversed 

 when the Allegheny plateau was raised to a sufficient elevation. 

 The only escape from such conclusion is in assuming that all the 

 teachings of our geologists, previous to this time, concerning 

 the succession of formations, are erroneous. While very many 

 errors, due to lack of data, have crept into our text-books, the 

 sequence of geological deposits in this region seems well estab- 

 lished. If not so early as herein intimated, these high-level val- 

 leys may still belong to a drainage period antedating either of 

 those discussed in these papers. 



Gerard Fowke. 



