AMERICAN GEOLOGY MAPLUREAN ERA, 1785-1819. 



231 



scientific men of his day, hud read and traveled extensively, and it may 

 he safe to assume that the views heid by him were supposed to rest 

 upon a good foundation, though they were not wholly accepted, as is 

 mentioned later. 



It was Mitchill's idea that the Great Lakes were the shrunken rep- 

 resentatives of great internal seas of salt water, which ultimately 

 broke through their barriers, the saline lakes becoming gradually 

 freshened by a constant influx of fresh water. The remains of the 

 barriers which held back for a time this inland sea he thought to be 

 still evident. One of them, he wrote, seemed to have circumscribed 

 to a certain degree the waters of the original Lake Ontario and to be 

 still traceable as a mountainous ridge be- 

 yond the St. Lawrence in upper Canada, 

 northeast of Kingston, passing thence into 

 New York, where it formed the divide 

 between the present lake and the St. Law- 

 rence, and, continuing to the north end of 

 Lake George, apparently crossed the Hud- 

 son above Hadley Falls. Thence he be- 

 lieved it to run toward the eastern sources 

 of the Susquehanna, along the Cookwago 

 and Papachton branches of the Delaware, 

 crossing the last named a little north of 

 Easton (Delaware Watergap), the Lehigh 

 north of Heidelburg (Lehigh Gap), and the 

 Schuylkill northwest of Hamburg in Penn- 

 sylvania. Continuing thence along to the north of Harrisburg. 

 across the Susquehanna, in a southwesterly direction until it entered 

 Maryland, and passed the Potomac at Harpers Ferry into Virginia, 

 where it became confounded with the Allegheny Mountains. Thence 

 gradually disappearing, traces of it appeared to the westward, as at 

 Cumberland Gap in Tennessee and the mountains west of Cape 

 Girardeau beyond the Mississippi. 



It is evident that for a good part of its course, as traced, this barrier 

 was but the Blue Ridge, while in eastern New York it was comprised 

 mainly of the Catskills and Adirondacks. 



To appreciate Mitchill's view, then, we have to imagine this now 

 broken and gapped ridge as continuous throughout its whole extent, 

 forming a vast dam holding back the waters of several salt inland seas 



early tendency to reprint many of the English works on geology and mineralogy. 

 This finds its most important illustration, from the present standpoint, in the reprint- 

 ing of Frederick Accums's A Practical Essay on the Analysis of Minerals (Philadel- 

 phia, 1809); Cuvier's Essay, as noted above; BakewelPs An Introduction to Geology 

 (New Haven, 1829); Cuvier's A Discourse on the Evolution of the Surface of the 

 Globe (Philadelphia, 1831) ; and De la Beche's A Geological Manual (Philadelphia, 

 1832), etc. 



Samuel Latham Mitchill. 



