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NEW YORK STATE MUSEUM 



markedly gabbroic. The analysis, however, shows a rock which, 

 in its high alumina and rather low iron and magnesia, is much 

 closer to anorthosite than to gabbro. It, nevertheless, represents 

 an intermediate stage in every single constituent. It was chosen 

 for analysis because of its freshness and in spite of the fact that 

 it appeared to be the most anorthositic portion of the Rand hill 

 body and therefore not a fair representative of its general char- 

 acter. The main rock is a more strictly intermediate one, and 

 the same thing is true of the Keeseville rock and of much of the 

 border of the great anorthosite mass of Franklin county. 



As close a calculation as can be made of the mineral composi- 

 tion of the anorthosite gabbro of analysis 3, without analysis of 

 the component minerals, indicates some 70$ of feldspar, made up 

 of orthoclase 7.5$, albite 29.75$ and anorthite 32$. In addition 

 there are 11.75$ of garnet, 7$ of augite, 4$ of hornblende, 2.5$ of 

 magnetite and 5$ of quartz. The free quartz is specially note- 

 worthy in so basic a rock, is usually to be found in the anorthosite 

 gabbro of the region, and recalls the quartz norites described by 

 Kolderup as associated with anorthosite in the Ekersund-Sog- 

 gendal district in Norway. For comparative purposes four of his 

 analyses are appended. 



1 2 3 4 5 



Si0 2 '. 53.42 52.61 52.21 53.28 51.62 



A1 2 3 28.36 27.15 19.24 23.3 24.45 



Fe 2 3 ] [1.65 



L 1.8 4.05 10.46 7.55 \ 



FeO J [5.3 



MgO 31 1.55 2.36 3.02 1.21 



CaO 10.49 9.96 7.28 5.01 9.97 



Na a O 4.82 4.53 3.48 3.9 3.49 



K 2 84 .78 1.09 1.51 1.27 



1 Anorthosite (labradorit), Ogne, Norway. Kolderup analyst. Die Labra- 



dorfelse des westlichen Norwegens. Bergens museums aarbog. 1896. 

 p.20. 



2 Anorthosite norite (labradomtnorit) , Ekersund. Kolderup analyst, p.20. 



3 Quartz norite, Soggendal. Kolderup analyst, p.16. 



4 Quartz norite, Theingsvaag bei Ekersund. Kolderup analyst, p. 16. 



5 Anorthosite gabbro, Carnes's quarry, Rand hill. 



It is to be noted that Kolderup's quartz norites are more 

 typical for the rock than the one analyzed from the Adirondacks, 

 that approaching anorthosite more closely and being more like his 



