Vol. 50.] 



basic eiujptive BOCKS OF CUtAX. 



27 



IV a. 



Camptonite, 

 M cen a. 



SiO, 41-90 



TiO" 2 4 34 



A1.,0 3 12-94 



Fe",0 3 1657 



MgO 925 



CaO 11-14 



Na.,0 262 



E 2 1-24 



100-00 



Table IV. 







Va. 



Average 



Average of eight 



Camptonite, 



of 



Camptonite 



Egge. 



IVa& Va. 



Analy. e . 



44-73 



4331 



43-65 



595 



5-14 



4-63 



13 08 



13-01 



16-29 



15-32 



1594 



14-7''. 



5-14 



723 



5-96 



12-29 



11-71 



1016 



2-32 



2-46 



3-05 



117 



1-20 



1-50 



10000 



100-00 



100-00 



In Table IV., parallel with the average of the camptonite 

 analyses from Ma?na and Egge, is placed the calculated average of 

 eight different camptonite analyses (from Campton Falls, Montreal, 

 Fairhaven, Proctor, Fort Montgomery, Mama, Egge, Hougen) : and, 

 as will be seen, the differences are not great. 



The following table (V.) shows the bostonite analysis from 

 Mama, calculated in the same manner ; for comparison I have 

 calculated the average of two American bostonite analyses (from 

 Shelburne Point and Champlain Valley) published by J. F. Kemp 

 (he. swpra cit.). . It will be noticed that the American bostonites 

 are richer in potash than the Norwegian. 



Table V. 



SiO., .. 

 Ti(X .. 

 A1.,0 3 

 Fe„0 3 

 MgO.. 

 CaO .. 

 Na 2 

 K,0 .. 



VI a. Bostonite, 



A, 



jerage 



of tivo American 



Mcena. 





Bostonite Analyses. 



60-57 







60-73 



0-91 









19-45 







21-00 



6-76 







3 83 



1-31 







0-79 



3-62 







4-44 



5-66 







4-52 



1-72 







4-69 



100-00 



100-00 



A simple calculation founded on the above data shows that a 

 mixture of 9 parts of the calculated average of the campton ites 

 from Mama and Egge, and 2 parts of the bostonite from Msena, 

 would make a composition differing very little from the above 

 calculated (p. 20) average composition of the olivine-gabbro-diabases 

 from Brandberget, Solvsberget, and Dignoes. 



