GEOLOGY OF THE NORTHERN ADIRONDACK REGION 



339 



company anorthosite and gabbro, and which Kolderup has so ex- 

 haustively described. In general the Adirondack syenitic rocks 

 run higher in the alkalis and lower in lime and magnesia than 

 the corresponding Norwegian rocks. These differences are but 

 slight, and the general agreement between the two series is very 

 close, but they point to a slight original difference in the char- 

 acter of the parent magma of the two districts. The appended 

 analyses bring this out clearly. 



1 2 3 4 5 6 



SiO, 57 57.11 63.45 64.35 68.5 70.33 



A1 2 3 16.01 17 IS. 38 15.46 14.69 15.59 



Fe 2 3 ] .42} 1-34 1.4 



L 10.3 12.48 j. 7.5 



FeO J 3.56J 3.25 1.54 



MgO 1.62 1.78 .35 .5 .26 1.3 



CaO 6.2 3.99 3.06 3.58 2.2 3.05 



Na 2 4.35 3.96 5.06 3.28 3.5 4.5 



K 2 3.53 2.59 5.15 3.54 5.9 1.29 



H 2 15 3 4 



Ti0 2 1.59 .07 1.63 85 



Zr0 2 MnO.l .24 



BaO 13 05 



Total 99.16 100.5 99.73 99.84 100.22 100.09 



1 Basic syenite from Natural Bridge; 7 of previous table. 



2 Monzonite from Fuldland near Farsund. Description and analysis by 



C. F. Kolderup. Die Labradorfelse des westlichen Norwegens, Bergens 

 museums aarbog. 1896. p.129. 



3 Augite syenite from Loon lake; 11 of previous table. 



4 Banatite from Dypvik near Farsund. Die Labradorfelse des westlichen 



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 microperthite in which the plagioclase mole- 

 cule is constantly in excess of the orthoclase, so that they 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 Adiron- 

 dack rocks and oligoclase in the Norwegian. Certainly the 



