332 



DEPARTMENT OF THE INTERIOR 



2 GEORGE V, A. 1912 

 Table XXII. — Comparisons of latites and monzonite. 



SiOo 



TiO"„ 



A1 2 3 



Fe 2 3 



FeO 



MnO 



MgO 



CaO 



SrO 



BaO 



NaoO \. .. 



K„0 



EUO- 



H 2 0+ 



P 2 6 



co„ 



FeSo and Fe- 8 



Rossland latites. 



■52 

 00 



•96 

 10 



■51 

 14 



•01 

 93 

 13 

 16 



•36 



•46 

 11 



•48 



•31 

 34 



•23 



Sierra Nevada 

 type latites. 



99-75 



■70 

 •06 

 •75 

 00 

 03 

 •06 

 •50 

 •02 

 02 

 19 

 •51 

 •58 

 ■30 

 •82 

 ■46 



100-00 



Average of 

 1 and 2. 



Average of 



world- 

 monzcnite. 



55 25 

 ■60 



16 53 

 3 03 

 437 

 •15 

 420 

 7-19 



3-48 

 4-11 



•66 



•43 



100-00 



100-00 



The close correspondence of the Rossland and Sierra Nevada averages 

 shows an essential identity of the magmas from which the respective lavas 

 crystallized; the justice of correlating the Rossland rocks with the latites is 

 clearly demonstrated. That latite should, as pointed out by Ransome, be 

 considered as the extrusive form of monzonite is indicated in the comparison 

 of Cols. 3 and 4. The two are not strikingly divergent at any point, yet there 

 are differences which together form the exact analogue of the difference 

 between the world's average syenite and trachyte, or the difference between 

 the world's average granite and rhyolite, or, in fact, between the world's 

 averages of any of the principal plutonic types and its generally recognized 

 effusive equivalent. In all these cases (as proved by the writer through actual 

 calculation; see chapter XXIV.), the effusive rock is the more salic and some- 

 what more alkalic; magnesia, lime, and iron oxides are characteristically lower 

 in the surface lava than in the corresponding plutonic. In all these 

 cases it would seem as if magmatic differentiation tends to be more 

 perfect when magma approaches and reaches the earth's surface, the 

 more salic pole naturally developing at the top of the volcanic vents where 

 it may be erupted as true surface lava. "Without further discussing this theore- 

 tical point we may conclude that petrography will gain by accepting fully 

 Ransome's highly useful conception of the latites as forming a group as 

 important among lavas as the monzonites are important among the plutonic 

 types. 



