100 NEW YORK STATE MUSEUM 



being developed as a side-hill quarry. 'The fractured surface of 

 the rock has a light green color with occasional mottlings of dark 

 green to black caused by uncrushed remnants of the feldspar. The 

 polished surface appears sea-green with the same mottling, but 

 showing also more or less the iridescence peculiar to labradorite. 

 Close inspection reveals fine specks and threads made up of red 

 garnet. A 12- foot diabase dike intersects the ledge in an east- west 

 direction. 



The second quarry, 1000 feet northeast from the former, is a pit 

 which at the time of the writer's visits was about 20 feet deep. 

 The stone is much coarser with more of the residual feldspar 

 crystals distributed through the mass. The jointing is in two di- 

 rections — northeast and northwest — with a horizontal series from 

 3 to 4 feet apart. Along two of the northeasterly joint seams have 

 been intruded dikes of trap and syenite porphyry, the former 3 

 inches and the latter 18 inches wide. 



The anorthosite is exposed on the west shores of Augur lake in 

 a series oi cliffs from 75 to 100 feet high. The sides of the cliffs 

 have been exposed directly to the weather ever since the glacial 

 period at least, yet the weathered stone is only a fraction of an 

 inch thick. This seems to indicate good resisting powers to frost 

 and agencies of decomposition. The jointing is very heavy, the 

 intervals often being 8 or 10 feet. Some of the rock contains 

 biotite in the place of the usual pyroxene. 



Microscopic examination. The general run of the stone from 

 the different localities may be described as composed of labradorite 

 in large part, the average being from 75 to 85 per cent. On account 

 of the frequent residual feldspar crystals, the grain would be called 

 coarse, although the groundmass itself is fine grained. The larger 

 feldspars are from 10 to 20 mm in diameter, with occasional in- 

 dividuals still larger. The principal dark mineral is diopside, which 

 appears emerald green in thin sections. Hornblende and biotite are 

 locally developed and take the place of the pyroxene. Garnet is 

 nearly always present in aggregates of small grains arranged about 

 the pyroxene, from which it has no doubt been derived in the 

 metambrphic process. Ilmenite is in small amount and an occasional 

 speck of pyrite can be seen. The decomposition products are kaolin 

 from the feldspar and chlorite from the ferromagnesian minerals. 

 They are not in sufficient amount to cause any noticeable weakening 

 of the structure. 



Physical tests. Specimens of the anorthosite were tested by the 

 office of public roads, United States Department of Agriculture, at 



