REPORT OF THE CHIEF ASTRONOMER 



705 



SESSIONAL PAPER No. 25a 



Table XLVL — Comparison of average analyses; granites and ground-mass of 



augite andesite. 





I 



2 



3 



4 





Ground-mass 



Average pre- 



Average 



pre- Cambrian 



granite 



of Sweden. 



Average 





(base) of augite 



Cambrian gran- 



granite of all 





andesite. 



ite of the world. 



periods. 





4 



47 



114 



236 



Number of Analyses. 











Si0 2 



69 31 



71 SB 



70-33 



70 47 



Ti0 2 





48 





54 





39 



AliO. 



17-11 



14 



20 



13 



86 



14 



90 



Fe 2 3 



215 



1 



47 



2 



19 



I 



63 



FeO 



■60 



1 



65 



1 



89 



1 



68 



MnO 







18 





26 





13 



MgO 



70 





59 





85 





98 



CaO 



2 63 



1 



98* 



2 



22 



2 



17+ 



Na 2 



3-20 



3 



26 



3 



19 



3 



31 



K 2 



430 



4 



53 



4 



41 



4 



10 



P 2 5 





10 





26 





24 









00 









100-00 



100 



100 00 



100 00 



* Includes 08% BaO and "01% SrO. t Includes 06% BaO and 02% SrO. 



The two comparisons suggest the speculation that the primitive acid shell 

 was derived from an andesitic magma, from the upper part of which most of 

 the femic material settled and enriched the lower part in the same oxides. The 

 complete mixing of these femic constituents in the hotter andesite below is 

 conceived to produce the basaltic shell. 



As far back as Keewatin time at least the acid shell seems to have been 

 largely or wholly solidified so as to be capable of Assuring, thus permitting the 

 basaltic Keewatin lavas to be extruded. With respect to all Keewatin and post- 

 Keewatin igneous action the basalt of the substratum has been hitherto called 

 ' primary,' but it is evidently possible that it was derived from a general pre- 

 Keewatin magma. The substratum basalt will still be referred to as primary, for 

 it bears the primeval heat and has suffered no appreciable chemical change of 

 composition since the oldest of the recognized pre-Cambrian basalts were erupted. 



Abyssal Injection of Magma. 



Proceeding on the assumptions : first, that the magmatic heat is chiefly 

 an inheritance from primitive times; secondly, that rock eruptible because hot 



