36 



NEW YORK STATE MUSEUM 



more silica and yet with nearly 15 per cent of dark silicates and 

 still others with less and larger percentages of the f erromagnesian 

 minerals. In the first two analyses given below, no. i and no. 3 are 

 probably not separate intrusions from the main anorthosite mass 

 but merely more ferromagnesian phases. No. 2, the Whiteface 

 type, is interpreted in the same way. It is not easy in these cases 

 to decide whether we are dealing with a separate intrusive mass 

 of mineralogy closely related, or not. Irruptive contacts against 

 the anorthosites have not been discovered and the location of these 

 varieties around the borders of the main mass leads to the inter- 

 pretation of them as rim facies. 



There are, however, at least two cases in which intrusive rela- 

 tions to the anorthosites can be demonstrated in more basic rocks 

 but ones of different type from the distinctively basic gabbros. 

 In the one case included fragments of anorthosite have been dis- 

 covered in the mass of gabbro; in the other irruptive contacts are 

 displayed. In both instances gneissoid structures have been sub- 

 sequently induced by pressure. 



ALOs . 



FeaOa . 

 FeO .. 

 MgO . 

 CaO . 

 NasO . 

 K2O .. 

 H2O+ 

 H2O— 

 CO2 .. 

 TiOs . 



S 



P2O5 . 

 MnO . 

 BaO • 



Pyroxenic 



morthosite, 

 Elizabeth- 

 town 



Pyroxenic 



anorthosite. Pyroxenic 



summit of anorthosite, 



Mt White- Giant trail, 



face Keene valley 



56.94 



53-18 



52.37 



20.82 



23-25 



24.68 



•83 



1-53 



1.24 



3-02 



1.82 



3-49 



2.36 



. 2.60 



2-00 



9.41 



II. 18 



10-57 



3-26 



3-97 



4-02 



1.58 



• 86 



• 86 



•59 



.98 



.90 



.21 



•15 





•45 



•34 





•44 



•45 

 tr 





•07 



.09 





.11 



.11 





•05 



100-24 100.51 



100.13 



Quartz . . . . 

 Orthoclase 

 Plagioclase 



Pyroxenes 

 Apatite • • • 



7.20 





Deficit . 90 



9-45 



S-00 



5-00 



61.10 



69.12 



80.52 



AbiAn2.2 



AbiAn2 



AbiAn2.64 



14-84 



15-36 

 .21 



12.86 



