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NEW YORK STATE MUSEUM 



The syenite from the southeastern area contains as essential min- 

 erals microperthite, a deep green nonpleochroic augite, small 

 amounts of hornblende and of quartz, with accessory apatite, mag- 

 netite, zircon and garnet, the last named perhaps secondary. 



The syenite from the area on the eastern shore of Schroon lake 

 contains relatively more hornblende and more quartz. 



In the Crown Point area labradorite is present in addition to 

 microperthite. 



Within the anorthosite area of the Blue Ridge, about a mile from 

 the boundary of the syenite, are three dikes which cut the anorthosite. 

 These dikes contain green augite, labradorite, and very abundant 

 garnet. They appear to belong with the syenite intrusion, and if 

 so, would indicate that the syenite is younger than the anorthosite. 



Anorthosite. Anorthosite is a coarse grained rock of the gabbro 

 family, presenting the extreme of the series rich in feldspar. Some 

 occurrences consist of pure plagioclase. 



In its massive phases the rock is quite fresh. The plagioclase is 

 twinned according to both pericline and albite laws. It is always 

 labradorite. Hypersthene, pleochroic from pink to green, and a pale 

 green, normal augite are the only other minerals which occur in 

 appreciable quantities. The structure is irregular, the bisilicates 

 being grouped together and not evenly distributed through the rock. 

 Associated with the grouping of constituents is a variation in size 

 of grain. When crushed, the dark patches are pulled out into len- 

 ticles, or into gneissoid banding. Similar sudden variations in tex- 

 ture have been noted by Professor G. H. W T illiams, in the Baltimore 

 gabbros. 1 



Hornblende, biotite and orthoclase may be present in small quan- 

 tities, with accessory or secondary magnetite, titanite, ilmenite, apa- 

 tite, chlorite, epidote, garnet, zircon and spinel. 



An extensive series of metamorphic effects can be seen. In the 

 northwestern portion of the quadrangle the rock is uniformly mas- 

 sive, except when brecciated by faulting. The labradorite crystals 



1 G. H. Williams. "The Gabbros and Associated Hornblende Rocks Occur- 

 ring in the Neighborhood of Baltimore, Maryland." U. S. G. S. Bui. 28. 



