596 Report of the State Geologist. 



Ill, but is notably paler in those of Series I and II. I expect to give the 

 subject of its formation detailed investigation in the future, as opportunities 

 occur. 



In distinction from the more feldspathic members of Series III, of which 

 special mention has been given above, often under the name anorthosite, 

 attention should be directed to the dark basic gabbros and their meta- 

 morphism. Although the latter are best exhibited in Moriah township, on 

 lake Champlain, just north of Port Henry, they are also, to a less degree, 

 shown in Schroon. The dark gabbros often contain olivine, and are a 

 plutonic rock, rich in pyroxene, brown hornblende, titaniferous magnetite, 

 and a dark green plagioclase that tends to develop somewhat lath-shaped 

 crystals and, in many specimens, to suggest the diabase type of texture. 

 Excellent exposures occur along the highways on the northeast at Nos. 104 

 and 103a. The last named is a large ledge, perfectly fresh and extensively 

 blasted out on account of the passage of the road. In the extreme southeast, 

 on the shore of Pharaoh pond, is a dike twenty-five feet wide, of well-marked 

 gabbro, far out from any visible parent mass, and in Avails of light grey 

 quartzose gneiss. Again, west of Schroon Lake post office, on the lane 

 leading out toward Rogers pond, at No. 84, is a fine outcrop of coarse dark 

 olivine gabbro. 



These massive gabbros. when subjected to shearing stresses, develop 

 dark hornblendic schists, and this change can be shown even in the limited 

 exposure of the rather narrow dike on Pharaoh pond. The feldspar is 

 crushed, and the dark silicates are dragged out into thin laminae. Even the 

 massive types have seldom escaped the production of reaction rims of 

 garnets that mark the boundaries between the feldspars and the dark silicates 

 or ores, almost never allowing the former to come into actual contact with 

 the latter. Hypersthene, brow n hornblende and biotite also enter into the 

 rims, especially where they surround magnetite, but garnet is much the 

 commonest and most noticeable of them all. 



Series IV. Much the most interesting and significant of all the 

 exposures in Schroon township is that embracing a few acres of w hat I take 

 to be the Calciferous formation. The rock is a grey, cherty limestone or 

 dolomite. It extends along the shore on both sides of the steamboat dock at 

 Schroon Lake post office, and has a total outcrop of about 400 yards. Rogers 

 brook falls over a ledge of it and affords the best and most extended cross- 

 section. The strike is by the magnetic compass N. 60° E., and the dip is 25° 

 X. W. Referred to the true meridian this would be 10 to 12° more to the 



