THE LOWER HURONIAN. 



367 



Assuming that this represents an isomorphous mixture of the diopside, hedden- 

 bergite, acmite, and fassaite molecules, and calculating their relative proportions, 

 we get approximatelj' the following result : 



Per cent. 



Diopside, Mg Ca SijOg 47 



Heddenbergite, Ca Fe Si A 27 



Acmite, Na Fe SiA 21 



Fassaite, Mg Al^SiO^ 5 



In the considerable percentage of the acmite molecule this augite approaches in 

 composition the pyroxene of the more alkaline rocks, the eleolite syenites. This 

 analysis very probably represents quite well the usual composition of the green 

 augite, as the proportion of zonal crystals, with colorless centers, and entire colorless 

 crystals, is small. The colorless augite is very similar to that of the well-known 

 augite granite from Laveline in the Vosges. 



The analyses of the anorthoclase feldspar and of the augite which are 

 quoted above show such a proportion of sodium oxide that one would 

 expect the granite itself to exhibit a very high ratio of that substance. This 

 proportion is shown in the following analyses,'' I being that of the normal 

 Cacaquabic granite facies as given by Grant, and II being that of the 

 granite-porphyry facies. 



Analyses of Cacaquabic granite and granite-porphyry. 



SiO^.. 

 TiOj . 

 PA-- 

 Al.Os- 

 Fe^Oj. 

 FeO.. 

 MnO. 

 CaO.. 

 MgO. 

 K,0.. 

 Na^O . 

 H,0.. 



Per cent. 

 66.84 



Per cent. 

 67.42 



Tr. 



18.22 

 2.27 

 0.20 



3.31 

 0.81 

 2.80 

 5.14 

 0.46 



Total. 



0.07 

 15.88 

 1.37 

 1.14 

 Tr. 

 3.49 

 1.43 

 2.65 

 6.42 

 0.05 



99.92 



f'Loc cit., p. 41. 



