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NEW YORK STATE MUSEUM 



cross the east and west section which he gives. During all the 

 writer's experience the mine has been full of water. 



Diamond drill cores on the surface near the Lee pit indicate 

 another dike in its northern extension and observations on the 

 surface show it to be a large one. It can be traced for a quarter 

 of a mile to the northeast. 



In this district the dikes have not shown more than 4 or 5 feet of 

 section in the mines. They are likely to appear at almost any 

 moment and they may be associated with small faults, but they 

 need never cause anxiety beyond this possibility. 



Dark basic gabbros. These rocks are widespread and yet in 

 less areal extent than the others whose description follows. They 

 seem to appear without any pronounced structural relationship, 

 but to have welled up as the last large product of the great igneous 

 activity. The diabase dikes are so much smaller that they are not 

 considered to be of the same order of magnitude. The gabbros 

 are dark green or black in color and have, when closely examined, 

 a faint pinkish cast from the quite invariable and richly dissemi- 

 nated small garnets, which are general throughout the mass in 

 the form of rims around the dark silicates and iron ores. The 

 chief component minerals are a dark green plagioclase, in rudely 

 tabular crystals, so thickly charged with dust of pyroxene and 

 spinel as to be at the best translucent in the slides; augite, which 

 is black in the hand specimen and green in the slide; hypersthene 

 of variable though sometimes large amount ; brown hornblende in 

 the same relations; and very abundant and sometimes relatively 

 large bits of titaniferous magnetite. The feldspars on the one hand 

 and the dark silicates and ores on the other almost never come 

 into actual contact, but are separated by the rims of garnet referred 

 to above, which course through the rock in faint pink bands. 



The gabbros almost always show some gneissoid foliation. In 

 extreme cases they pass into hornblende schists or amphibolites. 

 In large part the change is probably due to dynamic shearing 

 and dragging, but the banded alinement of the minerals may be 

 in part attributable to original flow structures. The gabbros 

 assume the form of intrusive sheets and irregular masses, whose 

 outlines can seldom be worked out sharply because of lack of 

 exposures. The railway cuts along Lake Champlain show that the 

 intrusive mass may tongue out into the Grenville limestone with 

 all manner of apophyses. Elsewhere single dikes are known, 

 although they are not sharply defined anywhere within the area 

 under discussion. In the maximum, the gabbros may cover as 



