Shaler.] 116 [February 1, 



arguments were presented, rather than the number of well-ascertained 

 facts which were adduced to support the theory, caused most geol- 

 ogists to give it their ready adherence. The criticisms of Mr. Charles 

 Hopkins, together with more extensive and careful study of mountain 

 chains, have caused a great decline in the estimation of this theory, 

 so that we may not now fear to run counter to a generally accepted 

 opinion in venturing to oppose M. de Beaumont's views. 



In a subsequent report I hope to embody the result of some obser- 

 vations made upon the western flanks of the Alleghanies, showing the 

 existence, in a position about as far west of their centre as the Rich- 

 mond axis is east of that point, of a mountain range, which, though 

 formed long anterior to the elevation of the principal mass of the 

 Appalachian chain, is still parallel to it, — may in fact be regarded 

 as the first step towards the formation of that singular mountain 

 system. 



Geologists have long known that the city of Cincinnati rests upon 

 an elevation of the silurian rocks of the Ohio valley, the beds dipping 

 gently away from that point. It has been always assumed that the 

 dip was uniform in every direction, giving a true dome character to 

 that elevation. Careful study of the region, however, has convinced 

 me that the elevation is not a dome, but has a north-east by north, 

 and a south-west by south trend, and extends as far as a similar ele- 

 vation of the silurian rocks, which is found in western Tennessee, 

 which elevation is, in fact, only the southern extremity of the Cin- 

 cinnati axis. The direction of the line connecting these isolated 

 patches of silurian rocks almost precisely coincides with the general 

 trend of the Appalachian chain to the eastward. There are many 

 reasons for believing that this Cincinnati axis was lifted above the sea 

 early in the silurian period. The presence of considerable quantities 

 of salt in the rocks of lower silurian age which flank this ridge, the 

 existence of ancient beach marks in the rocks of the same age, and 

 other phenomena, which cannot be properly discussed here, all point 

 to the conclusion that this ridge was formed at a time when the silu- 

 rian period had just begun, and while a large part, if not the whole, 

 of what is now the highest part of the Alleghanies was still beneath 

 the level of the sea. The existence of ridges of widely different ages 

 on either side of the Appalachian chain, makes it questionable 

 whether the central mass of that system is to be all referred to the 

 same period as has hitherto been done ; whether it may not be rather 

 a congeries of elevations dating from periods of various- ages, between 



