REPORT OF THE DIRECTOR AND STATE GEOLOGIST 1900 Vll 



near Keeseville and on Rand hill in Clinton county, the latter 

 furnishing the rock whose analyses appears in column 3, are very 

 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 anortho'site gabbro of analysis 3, without analysis of 

 the component minerals, indicate some 70^ of feldspar, made up of 

 orthoclase 7.5^ albite 29.75^ and anorthite 32^. In addition there 

 are 11.75^ of garnet, 7fo of augite, 4^ of hornblende, 2.5^ of mag- 

 netite and 5fc of quartz. The free quartz is specially noteworthy 

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

 of the region, and recalls the quartz norites deiscribed by 

 Kolderup as associated with anorthoisite in the Ekersund-Sog- 

 gendal district in Norway. For comparative purposes four of his 

 analyses are appended. 



12 3 4 5 



SiOg 5.3.42 52.61 52.21 53.28 51.62 



AI2O3 28.3'6 27.15 19.24 23.3 24.45 



FegOs ) (1.65 



> 1.8 4.05 10.46 7.55 < 



FeO ) (5.3 



MgO 31 1.55 2.36 3.02 1.21 



CaO 10.49 9.96 7.28 5.01 9.97 



NagO 4.82 4.53 3.48 3.9 3.49 



K2O 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 (lahradoritnorit), 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, Oarnes's quarry, Rand hill. 



