r38 NEW YORK STATE MUSEUM 



inch; the scapolite zone evidently marks the strip of maximum 

 disturbance and change. 



At 3J miles is another long cut, 140 yards in length. At the 

 west end is a dike of gabbro (954B) 8 feet wide, of interest from 

 several points of view. It contains some 30'^ to 40^ of augite, 

 hornblende, bronzite, magnetite and apatite, some little quartz, 

 and garnet rims of the honeycomb type between the magnetite 

 and feldspar. The feldspar is largely of the blotchy intergrowth 

 type, but considerable plagioclase remains, sufficient to shaw 

 that it is andesin and that it alters to the other feldspar. There 

 is much unaltered andesin in the ground mass however, and this 

 seems to have been largely recrystallized. Again, in this cut is 

 abundant evidence of slip faulting along one set of the joints. 

 Here the larger cracks contain anorthosite fragments cemented 

 by deposition of calcite followed by chalcedony. These vein fill- 

 ings are mostly only fractional parts of an inch in width, occa- 

 sionally reaching 2 or 3 inches. 



At 3f miles is another long cut 180 yards. Neither this nor 

 the previous one is a continuous cut, but shows low anorthosite 

 ridges, with summits some dozen feet above the roadbed, sep- 

 arated by sand-filled depressions. The rock here (9i5'5) is the 

 same shattered anorthosite of the previous cuts. Garnet is more 

 prominent, and the rock is not quite so prevailingly feldspathic. 

 Near the west end of the cut is a probable inclusion of coarse 

 granite. At 4 miles is a small cut exposing very coarse anor- 

 thosite, much less shattered than the foregoing. 



Summary of section. This section will answer for the type of 

 many well within the anorthosite mass. Except for occasional 

 intrusions of gabbroid rocks and inclusions of granite the rock 

 shows great uniformity. The feldspar is pretty uniformly an acid 

 labradorite with extinction maxima of 20° to 22°, but in nearly all 

 cases there is some little of the untwinned feldspar intergrowth 

 present. This may become of quite respectable amount, as illus- 

 trated by exposures some 3 miles south of the line of the section, 

 between Upper Saranac lake and Follensby Clear pond, where the 

 rock is slightly more gabbroic. In fact, increase in amount of 



