34 



NEW YORK STATE MUSEUM 



The results show that quartz may be expected in the moderately 

 silicious ones although it may not be sufficiently abundant to catch 

 the eye of the observer. The orthoclase molecule is also seldom 

 visible in the slides. The plagioclase lies near the labradorite series 

 but when the anorthite molecule passes the 2. ratio it approximates 

 bytownite. The overwhelming percentage of the feldspar is ap- 

 parent. The anorthosites are rich in the light colored minerals 

 beyond the vast majority of eruptive rocks. To what extent the 

 ferromagnesian molecules are to be assigned to diopside and 

 h3^persthene is not apparent. Microscopic study proves both to be 

 present but their total is small at best. 



We have thus to deal with a great eruptive magma, containinp, 

 little else than silica, alumina, lime and soda. Although the lirsv 

 to appear in a series it is probably a differentiation product from 

 an earlier original richer in iron and magnesia. The later residual 

 outbreaks profited by these accumulated bases which were left 

 behind. 



Inclusions. In the bare ledges along Coughlin and Stevens 

 brooks which flow eastward down the eastern buttress of Giant 

 mountain several cases of included fragments of older rocks, un- 

 doubtedly belonging to the Grenville series have been discovered. 

 Figure 4 illustrates the shape and size of one. They have uni- 

 formly a garnetiferous border marking their boundaries against 



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10 H 



Fig. 4 Fragment of quartziLe, included in anorthosite. Bed of Coughlin brook, about 

 I mile west of highway. 



