GEOLOGY OF THE NORTHERN ADIRONDACK REGION 331 



Falls outlier, and hence younger. But he has so far met with 

 no instance of gabbro cutting the syenite masses in the north, nor 

 of cutting the distinctly later granites, though many cases are 

 known in Avhich granitic gneisses of uncertain age are cut. This, 

 together with the fact that there is no evidence to show that the 

 syenite at Little Falls is of the same age as that to the north, 

 causes hesitation in regard to the relative ages of the sye- 

 nite and gabbro there. It is thought to be highly probable how- 

 ever that the gabbro is the youngest rock, and that the order of 

 appearance of the great intrusions was, first anorthosite, followed 

 in order by syenite, granite and gabbro. 



Chemical analyses. A sufficient number of chemical analyses of 

 the rocks of the great intrusions have been made to give a very 

 fair idea of their range in composition, and to show their close 

 relationship to one another. To date, analyses of the later gran- 

 ites wholly fail so far as the writer is aware, and hence the more 

 acid members of the group are lacking. But their mineralogy 

 indicates a close relationship to, and gradation into the others 

 through the medium of the acid syenites, and it may be confidently 

 stated that their analyses will fall regularly into the series, and 

 show a regular gradation from the acid syenites through ordinary 

 granite to the very acid Morris granite. 





1 



2 



3 



4 



5 



6 



7 



SiO, 



. . 44.77 



47.42 



51.62 



54.47 



54.62 



54.38 



57 



AI2O3 



12.46 



17.34 



24.45 



26.45 



26.5 



20.53 



16.01 



Fe^Os 



4.63 



4.91 

 10.22 



1.65 

 5.3 



1.3 

 .66 



.75 



.56 



2.78 1 

 5.5 I 





FeO 



. . 12.99 



• 10.3 



MgO 



5.34 



5.21 



1.21 



.69 



.74 



1.99 



1.62 



CaO 



10.2 



8.09 



9.97 



10.8 



9.88 



5.39 



6.2 



Na^O 



2.47 



3.48 



3.49 



4.37 



4 5 



5 2 



4 35 



K2O 



.95 



1.89 



1.27 



.92 



1 '>S 



3 4 



3 53 



H,0 



.6 



1.13 



.72 



.53 



.91 



.5 



.15 



CO, 



.37 















TiO. 



5.26 



3.6 









.09 





P,0o 



.28 



.06 



.01 







15 





CI 





.21 









.03 





F 













.03 





S 



.26 















MnO 



.17 



.06 



.1 







.01 





BaO 



trace 



.04 









.16 





Total . . . 



.. 100.75 



100.01 



99.79 



100.19 



99.7 



100.03 



99.16 



Sp. gi- 



3.09 





2.798 



2.72 



2.7 



2.7 





