ADIRONDACK MAGNETIC IRON ORES 6l 



of Swedish type. Explorations with the diamond drill then 

 follow. 



From Mineville southward through Moriah Center, Moriah 

 (locally called " The Corners ") and still farther, the mantle of drift 

 extends with comparatively few exposures of the bed rock. Just 

 east of Moriah Center, Mill brook has cut into it fully ioo feet 

 without reaching the rock bottom. Presumably the expiring 

 glacial activity filled the valley and the movement was probably 

 from the northeast since such scratches as remain in the general 

 region run n. 5o°-6o° e. The boulders seldom attain the gigantic 

 size sometimes shown farther within the mountains but individ- 

 uals up to 6 or 8 feet are not uncommon. 



Paleozoic sediments. These strata are practically limited to the 

 lake shore in the region under consideration. The Potsdam pro- 

 jects up the valley of McKenzie brook for perhaps half a mile from 

 the water, but ceases long before it is concerned with any mines. 

 No further mention is therefore made of any of them. 



Diabase dikes. These interesting narrow bodies of dark basaltic 

 rock are widespread and of no small scientific interest. Through- 

 out the Adirondacks they appear not uncommonly in the mines, 

 and usually occupy a fault line by which the ore is thrown varying 

 distances up to 30 or 40 feet. They strike in two principal direc- 

 tions, a northeast set, embracing about three quarters of the known 

 instances and an east and west set, including almost all the rest. 

 In only one or two instances have they been observed with a north- 

 west strike. These directions correspond with the chief structural 

 breaks, and undoubtedly in seeking a path to the upper world the 

 dikes have merely followed the lines of least resistance. 



At Mineville, one, with an east and west strike is known in the 

 Joker working; two or three, with a northeast strike cut the Har- 

 mony bed; one appears in the Miller pit, which is probably con- 

 tinuous with one of those in the Harmony bed, and another was 

 reported from the Old Bed workings in former years. The rocks 

 are all badly decomposed and not in good condition for careful 

 determination. It is necessary to exercise care lest the darkened 

 and chloritized breccias along faults be mistaken for them. 



In the Cheever mine a number of dikes were met in former years 

 and have been figured by B. T. Putnam. 1 The strike is not 

 recorded and may be judged only from the fact that the dikes 



1 Report on the Mining Industries of the United States, Tenth Census, 

 v. XV. 



