244 JS/otes on American Geology. 



Oswego county and forms the banks of Salmon river. Not a 

 single species of shells or plants is common to both. The former 

 is highly inclined, and on its edges rests mTConformably the cal- 

 ciferons sandrock of Eaton, then follows the sparry iimerock of 

 the same author, with some fossils peculiar to it ; above that the 

 limestones and shales of the Trenton series, several hundred feet 

 thick, and then the Salmon river sandstone follows in the as- 

 cending order. This shows the great danger of error in endeav- 

 oring to identify strata over large areas, if we neglect to appeal 

 to the evidence afforded by palasontology, and rely too exclu- 

 sively upon the ever varying mineral composition of rocks, which 

 it is obvious may present similar features in groups of widely 

 different age. 



The present grand undulations or inclined planes of the sur- 

 face of the United States, considered in reference to their broader 

 outlines, are owing to the position which the transition have been 

 compelled to assume, by the unequal rise of primary chains. This 

 has arisen from its vast aggregate thickness and enormous unin- 

 terrupted extent. Beginning, as it does, on the border of the 

 Arctic sea, it extends, in some parts of its range, unbroken by 

 granite peaks, quite to the center of Alabama, while~ it extends 

 east and west, from the Appalachian chain to Engineer canton- 

 ment on the Missouri river. It, therefore, on a rough estimate, 

 will be two thousand four hundred miles north and south by one 

 thousand four hundred in extent east and west. 



The upheaving force, acting over so vast an area, has only 

 next the mountain chains greatly disturbed and inclined the strata, 

 leaving the mass nearly horizontal to the eye, but rising and fall- 

 ing in enormously extended, slightly inclined planes and undula- 

 tions. It is to the re-entering angles or synclinal lines of the 

 planes that we owe the course of many of our large rivers. East 

 of Little Falls on the Mohawk, that river runs many miles in a 

 depression caused by the gentle dip of the strata on the north 

 bank, and their gentle rise on the south. The St. Lawrence 

 flows in a profound synclinal line, as may be seen by reference 

 to Mr. Emmons' section in the New York geological reports for 

 this year. Dr. Hildreth informs us, that the formations in Ohio 

 dip towards the center of the valley of the Ohio river, and as 

 they reappear at higher levels in Kentucky, there can be no doubt 

 a synclinal line has determined the original course of that river. 



