488 H. p. GUSHING ^ASYMMETRIC DIFFERENTIATION IN SYENITE 



position of a mixture of this rock with a normal syenite (analysis 11) 

 in proper proportion to give a silica percentage equal to that of the basic 

 syenite of analysis 7 is presented for comparison with the rock itself. 

 This mixture would consist of 58.3 per cent gabbro and 41.7 per cent 

 syenite. These relative percentages of the gabbro and syenite form 

 columns 1 and 2, their sums give the composition of the mixture in 

 column 3, and in column 4 is the analysis of the basic syenite for com- 

 parison. The two iron oxids are put together and only the principal 

 oxids included in the table. 



SiOj. . 



AljO;) 



re.,0, 

 MgO. 

 CaO. . 

 Na^O. 

 K,0. . 



1 



2 



3 



4 



27.65 



26.45 



54.1 



54.1 



10.11 



7.66 



17.77 



17.45 



8.82 



1.66 



10.48 



10 99 



3 04 



.15 



3.19 



2.33 



4.72 



1.27 



5.99 



6.17 



2.03 



2.11 



4.14 



3.81 



1.1 



2.15 



3.25 



3.06 



57.47 



41.45 



98.92 



97.91 



+ .32 



— .51 



+ .86 



— .18 

 + .33 

 + .19 



In view of the many uncertainties connected with the calculations, it 

 has not been deemed necessary to recalculate the footings to 100 per cent. 

 It is thought that they show just as clearly the size and importance of 

 the discrepancies as they stand as if so recalculated. Though there is 

 a considerable difference in the magnesia percentage of the two, it is 

 not thought to be of a higher order than the differences in magnesia 

 content shown by the rocks of both classes of similar silica content when 

 followed from place to place. The other differences are certainly of no 

 higher order. The calculation is therefore thought to indicate that in 

 this instance the chemical evidence is not opposed to the suggested hy- 

 pothesis. Neither the gabbro nor the syenite used in the calculation are 

 from the immediate region, though it is thought that each could be 

 closely duplicated there. Each rock also varies considerably from place 

 to place, and it is an open question whether the syenite and the gabbro 

 from the Tupper Lake region would or would not have furnished a 

 closer agreement had analyses been available. 



This very basic syenite is not the average variety of the basic rock, 

 but the most extreme type met with which furnished material sufficiently 

 fresh for chemical analysis. The only available analysis of syenite of 

 more average basicity is that from the syenite intrusion inlying in the 

 anorthosite nearly midway on the northern border of the map. The 



