EEPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 v77 



4 Banatite from Drpvik near Farsimd. Die labradorfelse des west- 



lichen Norwegens, p. 123. 



5 Quartz augite syenite from near Willis pond; 14 of previous table. 



6 Adamellite from Farsund. Die labradorfelse des westlichen Norwegens, 



p. 115. 



So far as their mineralogY is concerned, the Adirondack rocks 

 would fall without question in the monzonite group. The pre- 

 vailing feldspar is miicroperthite in which the plagioclase molecule 

 is constantly in excess of the orthoclaee, so that thej are strictly 

 plagioclase- orthoclase rocks. The table brings out the chemical 

 differences, which would seem mainly due to the fact that the 

 plagioclase in the microperthite is albite in the Adirondack 

 rocks and oligoclase in the Norwegian. Certainly the Adirondack 

 rocks closely approach the monzonite type. They also closely 

 approach Broggers akerite type (quartz augite syenite) from near 

 Christiana, and seem to occupy a position intermediate between 

 the two. Smyth's rock from Xatural Bridge, column 1 of the 

 above table, would certainly fall within the monzonite group, 

 notwithstanding its high lime percentage; and the rock from 

 north of Tupper lake, column 9 of the original table, belongs also 

 in that group lying on the border land between monzonite and 

 banatite.i Because of this, it is perhaps more logical to refer 

 all the Adirondack syenite to that group, though as a somewhat 

 abberrant type. 



It would therefoTe appear that in each district a very similar 

 magma has given rise to a very similar rock series, and, it is 

 likely, through a similar differentiation process. The order of 

 succession of the different types can not be compared, since the 

 Adirondack succession is uncertain in one respect. The syenite 

 followed the anorthosite, and then came the granite, but the 

 position of the gabbro is uncertain. It is certainly later than the 

 anorthoisite, and certain gabbroic dikes which have been found 



^ The monzonite group was established by Brogger to contain rocks 

 intermediate between the granite syenite group (orthoclase rocks) on the 

 one hand, and the diorite gabbro group (plagioclase rocks) on the other; 

 hence characterized by both orthoclase and plagioclase. Monzonite has 

 a silica percentage between 50^ and 00^, banatite between 60;^ and 66;^, 

 and adamellite over 66^. 



