108 NEW YORK STATE MUSEUM 



tures of the topography about Lyon Mountain and the distribution 

 of the magnetite deposits. The deposits indicated by the numbers 

 on the map are as follows: i, Stan dish or 81 mine; 2, Phillips vein; 

 3, Main group; 4, Parkhurst. 



General geology 



The several prominences, which include Lyon mountain in the 

 middle, Averill peak and Morton's peak on the western flank and 

 the Dannemora mountain on the east, constitute the main axis of 

 elevation in this section of the Adirondacks. Towards the east the 

 ridge is succeeded by the narrow abruptly sloping plain of Lake 

 Champlain, while on the north the elevations gradually die out 

 beneath the broad plain of the St Lawrence. Lyon mountain, the 

 culminating point, rises to an altitude of 3,800 feet, and is the most 

 conspicuous landmark in the northern Adirondacks. The ridge is 

 separated from the parallel one to the north, known as Ellenburgh 

 mountain, by a valley 5 or 6 miles wide, the floor of which lies at 

 an elevation ranging from 1500 to 1700 feet. On the west the 

 valley contracts owing to a line of spurs which offshoot from Averill 

 peak in a northwesterly direction. Upper Chateaugay lake which 

 receives the drainage of the valley lies in the western part while 

 Chazy lake is on the eastern side of a low ridge that extends 

 northeast from Lyon mountain. 



The higher ridges mentioned above mark the limits of the gneisses 

 and associated crystalline rocks in the northeastern Adirondacks. 

 As they fade out into the bordering plains, the crystallines are suc- 

 ceeded unconformably by Paleozoic sediments which extend over 

 the remaining area as far as the shores of Lake Champlain and the 

 St Lawrence river. The present line of contact between the two 

 series is well up on the outer slopes of the ridges but follows the 

 main valleys for considerable distances into the interior. 



Paleozoic rocks. Within the area under discussion the Paleozoic 

 strata are of little areal importance. A narrow belt of Potsdam 

 sandstone occupies the lower part of the depression between Ellen- 

 burgh and Dannemora mountains extending as far as Chazy lake 

 and to an elevation of about 1500 feet. Another Potsdam area 

 occurs on the northeastern border of Dannemora township where 

 it is found as high as 1700 feet. According to H. P. Cushing, 1 who 

 has mapped the areas, the rock is a reddish arkose quite different 

 from the coarse phase usually occurring at the base of the formation. 



1 Geology of Clinton County. N. Y. State Mus. 49th An. Rep't. 1898. 

 2:537. Also Geology of Rand Hill, 53d Mus. Rep't. 1901. 1:63. 



