17 



west of the Mississippi, founded on the im- 

 perfect data at that time in his possession, 

 have been verified by travellers who have 

 subsequently explored these regions. 



Much of this outline has been filled up by 

 the labors of succeeding geologists in differ- 

 ent sections of the Union, and the materials 

 for this purpose are daily accumulating. 

 Among the most important of these we may 

 particularize the various geological notices 

 of Dr. Mitchill in the Medical Repository^ 

 and more at large in the appendix to an 

 edition of Cuvier^s Preliminary Essay^ pub- 

 lished in this city in 1818. From the pre- 

 sence of marine organic relics in the soil 

 and rocks adjacent to the great lakes, the 

 learned professor conjectures that the ocean 

 once filled the basins of the latter, and co- 

 vered the surface of the former. He has 

 exercised much ingenuity in tracing the 

 barriers of this imaginary inland sea, and 

 has indicated the principal spots where 

 breaches are supposed to have been made, 

 which drained the extensive country now 

 included in the states of New- York, Penn- 

 sylvania, Ohio, and part of Virginia. The 

 alluvial described by Maclure, is extended 



c 



