Washington — Charnockite Series of Igneous Rocks. 327 



contain the fusiform inclusions just mentioned. As the norm 

 shows that a much greater amount of the anorthite molecule is 

 present than is accounted for by the actual proportion of 

 obvious andesine present, a very considerable proportion of the 

 "unstriated, and hence apparently alkalic feldspar, is probably 

 sodicalcic. This supposition was confirmed by an examination 

 kindly made by Dr. !S y . L. Bowen, which showed that a great 

 majority of the feldspar grains had a refractive index of about 

 that of Ab 3 An 1 . 



The pyroxene is entirely a hypersthene, in subhedral and 

 often somewhat rounded grains. These are colorless, but with 

 a distinct pleochroism : c slightly bluish gray, o and b pale 

 pink. The parallel cleavage cracks are rather coarse, and here 

 also many individuals show oblique extinction. There is no 

 hornblende or biotite. Magnetite is more abundant than in 

 the preceding type, as small, highly irregular masses mostly 

 interstitial between the other minerals, and seldom included in 

 them. There are a few very small prismoids of apatite. 



The mode, determined by Rosiwal's method, is approximately 

 as follows, no distinction being made between the twinned and 

 untwinned feldspars. 



Quartz 15*5 



Feldspar _ 55*5 



Hypersthene . . 23*6 



Ores 5*4 



On comparison with the norm it would appear that a little 

 quartz has been overlooked — or that it is possibly occult, and 

 that some of the anorthite molecule has gone into modal 

 pyroxene. 



The two analyses A and B were made on specimens with 

 the same number, so that practically identical composition 

 between them may be assumed ; but there are some discrep- 

 ancies between the two analyses. The higher " A1 2 3 " in B 

 may be accounted for by the non-determination of Ti0 2 and 

 P 2 5 and also probably by the co-precipitation of some MgO.* 

 The higher CaO in B is more difficult to account for. With 

 these exceptions the two analyses agree very well. 



The norm of A is as follows : 



Q 20-95 



Or 6-67 



Ab 31-44 



An 20-57 



Di 1 -36 



Hy 13-74 



Mt 3-25 



II 1-52 



*InA, A1 2 3 + Ti0 2 + P,0 5 + MgO = 19-07 ; in B, A1 2 3 + MgO = 18*79. 



