52 



ROCKS OLDER THAN THE TACONIC SYSTEM. 



Hoosic or Green mountain on the east. The succession of this lower division is represented 

 by an actual section extending from Glen's falls five miles northeast, or to tlie primary 

 upon which the Potsdam sandstone rests. 



Fig. 1. 



a. Granite; 6. Potsdam sandstone ; c Calciferous sandstone ; d. Trenton limestone; e. Black marble, extending 



towards the river. 



The gorge at this place is not sufficiently deep to expose the Potsdam sandstone, but the 

 succession is well exliibited in passing over the coimtry in tiie direction stated above. The 

 Utica slate at tiie falls has been mostly destroyed by denudation ; but it appears both above 

 and below, upon the river banks, with its characteristic fossils, succeeding the Trenton 

 limestone. 



The point to be shown, is tliat the lower division of the New-York system reposes upon 

 some of the members of the Taconic system ; that is, to show by actual superposition that 

 the former rests upon the latter. I trust I shall be able thus to do : not only to point out 

 where the two systems approach each other so closely that there is but little space inter- 

 vening between them, but where the finger may be placed directly upon the line of 

 demarkation ; tlie one being the inferior and unconformable, and the other the superior. 

 This great fact being shown, its bearing on American geology is not confined to one or 

 two subjects, as metamorphism and age ; but it is also important as furnishing a base from 

 which may be formed a general nomenclature of sedimentary rocks. At any rate, it is a 

 point to be established before a nomenclature can be devised, that shall express the order 

 in which the series follow each other, and the designations proper to apply to them. 



^ 4. Rocks bklow and older than those constituting the taconic system. 



In Massachusetts and Vermont, as well as in New-York, what has been usually deno- 

 minated the Prhnnry range skirts the Taconic system upon the east, and forms with it 

 parallel belts of low mountain ridges, whicli unitedly form the Green mountains. Different 

 portions have received different names ; as Hoosic mountain, immediately east of Adams 

 in Berkshire (Massacliusetts) ; and Mansfield mountain, to the east of Burlington (Vermont) . 



The Taconic range is parallel with the main ranges constituting the Green mountains, 

 and is a few miles only to the west. The ridge dividing New-York from Massachusetts is 

 the one to which this name was originally given. The ranges are, however, connected 

 by spurs, though not so intimately as to destroy the integrity of either, and make it 

 necessary to merge them both in one main range. The name Gree^i mountains is a more 



