ESSEX COUNTY. 267 



Tlie lowest of this class of rocks is the potsdam sandstone, the southern limit of which is 

 at Ticonderoga, where it occupies a limited area upon the platform above the falls, and below 

 the outlet of Lake George. It occupies the western base of Mount Defiance. It dips to the 

 northwest, and appears again at the village in Ticonderoga. The whole tliickncss of the rock 

 is about one hundred feet. It is crystalline in the mass, being divided into coarse rhombic 

 prisms. I am unable to speak of its extent northwards ; it, however, probably lines the shore 

 of the lake for some distance towards Crownpoint. At the latter place, the primary extends 

 to the lake on the west side, and separates this portion of the sandstone south from that at the 

 north. 



The sandstone reappears two miles north, and is brought up by an uplift bearing the calci- 

 ferous sandrock : it occupies but a small space, and dipping north, it disappears beneath the 

 calciferous. Adjacent to the base of Bulwagga mountain, it appears again from beneath the 

 tertiary clays and calciferous, forming a belt about one mile wide. 



Again, it appears at Cedar point, and lines the shore, with a northerly dip, for about one 

 mile. It is well characterized at this place, but is merely a narrow belt, about one-fourth of a 

 mile wide. It occurs here in a form and condition to be employed for the hearths of furnaces. 

 It extends a few rods north of the furnace at Port Henry, bearing, however, the calciferous. 

 Here it terminates in a rocky point, and appears resting against the primary limestone. The 

 primary again interrupts its progress northwards, but it reappears under the same characters 

 tvi'o miles north, and continues a mile or two, when it is succeeded by the calciferous sand- 

 rock and chazy limestone. At Westport, it reappears again, occupying the banks at the 

 landing, but continues only a few rods northward, when the primary once more reaches the 

 lake shore, and from thence they occupy it to the exclusion of all sedimentary rocks, as far 

 as Split-rock. 



The potsdam sandstone does not appear again upon the west side of the lake south of Port 

 Kent. Four miles west of Essex village, it appears, reposing against the hypersthene rock 

 near Ross's bridge. Here I found the lingula peculiar to this rock. 



The only locality which now requires a special notice, is at Port Kent, where it appears in 

 considerable force. From Port Kent, it extends west from the lake between six and seven 

 miles, and it is in this vicinity that it presents the greatest interest and importance. 



The Ausable river, which, for some distance forms the boundary between Essex and Clin- 

 ton counties, flows through deep and frightful chasms in this rock. For two miles, at least, 

 this large and rapid river is compelled to flow through a rocky chasm with perpendicular 

 walls of one hundred feet, with a width only varying from twenty to forty feet. A most 

 interesting point for examination is at Birmingham, at the place called the High bridge. At 

 this place, a flight of stairs has been made and placed for the convenient descent to and ascent 

 from the bottom of this gorge. It is one hundred feet deep at this place, and the rocks are 

 rent and broken in the manner represented in the sketch at the commencement of this article, 

 (fig. 67.) 



