ADIRONDACK MAGNETIC IRON ORES 0,1 



General geology 



The higher Adirondack ridges do not extend much beyond the 

 Clinton county line. The Ausable in its course from the east and 

 west branches to Lake Champlain marks the limit between the 

 region of main uplift and the bordering foothills. South of the river 

 the surface rises quickly to the level of the flanking ridges which is 

 less than 1500 feet, and thence abruptly with frequent rock scarps 

 to the interior prominences which increase in hight toward the 

 southwest and merge into the central dominating range of Essex 

 county. On the north side, a terraced sand plain intervenes between 

 the river and the first ridge forming the valley wall. In the stretch 

 from Ausable Forks to Clintonville it is from 1 to 2 miles wide but 

 contracts below the latter place where the valley becomes very 

 narrow. The hight of the ridge on which the mines are situated 

 for the most part averages about 11 00 feet or 500 feet above the 

 level of the plain. 



The anorthosites and associated gabbros which are so widely 

 developed to the south do not occur in force across the Clinton 

 county line. They compose, however, the higher prominences 

 within a short distance of the Ausable and in the vicinity of Keese- 

 ville, east of Clintonville, even extend somewhat over the line as a 

 narrow tongue diminishing in width toward the north. They have 

 no bearing upon the iron ores and will not be further considered. 



Gneiss series. The area surrounding the ore bodies is underlain 

 chiefly by an acid augite gneiss, a part of the basal gneiss series 

 (Saranac formation) which borders the northeastern Adirondacks 

 and shows much uniformity of character throughout the area. 

 Bands of darker gneiss and pyritous schists that can be referred 

 to the sedimentary or Grenville series occur rarely and in limited 

 outcrops. Of recognizable igneous rocks there are small exposures 

 of syenite, gabbro and diabase, all intrusive in the gneiss and thus 

 of later age. 



The gneiss presents some variations from place to place, but the 

 differences either in structure or composition are seldom so pro- 

 nounced that a basis for a classification is afforded. The extremes 

 are connected, moreover, by transition phases and are intimately 

 associated in .their field occurrence. 



In its composition, feldspar, augite and quartz partake most 

 largely. The feldspars may be microperthite, orthoclase or micro- 

 cline among the alkaline varieties which are the prevailing ones or an 

 acid plagioclase. Microperthite and orthoclase are commoner than 

 the other varieties and their reddish color gives the predominant 



