ELIZABETHTOWN AND PORT HENRY QUADRANGLES 55 



forms basic centers around which are grouped the bisilicates in 

 especial richness. In several places the titaniferous magnetite has 

 become sufficiently concentrated to attract attention as an iron ore. 

 The ore yields about 40 per cent iron more or less, and can be best 

 discussed under the topic iron ores. It is simply a portion of the 

 gabbro mass with an unusual amount of the titaniferous magnetite. 

 The feldspar fails but all the other components are distributed 

 through the ore and appear in the thin section. 



The reaction rims of garnet are very widespread in the gabbros, 

 so much so that it is unusual to find the rock unprovided with 

 them. They follow along the border lines between the feldspar and 

 the more basic minerals, preventing the contact of the two, and 

 giving a pinkish cast to the rock which is quite characteristic. The 

 garnets at times manifest a curious tendency to develop projections 

 like fingers out into the feldspar and seem to have formed from 

 one twin lamella and not from those on either side. 



A number of analyses of the gabbros were prepared several years 

 ago in the laboratory of the United States Geological Survey, in 

 connection with a paper by the writer, upon the " Titaniferous 

 Ores of the Adirondacks."^ They are reproduced here in order to 

 give an idea of the chemical composition of the rock and to fur- 

 nish a basis for recasting into the approximate percentages of 

 component minerals. With these quoted analyses are one or two 

 others from exposures not connected with ore bodies and only 

 hitherto published in Bulletin 168, United States Geological Survey, 

 page 37 under the work of the chemical and physical laboratories. 



_._ I 2 3 4 5 



SiOo 47.88 47.16 46.74 44-97 44-77 



AJ2O3 18.90 14-45 16.63 15.40 12.46 



FeaOs 1.39 1.61 2.17 2.29 4.63 



FeO 10.45 13.81 10.60 12.39 12.99 



MgO 7.10 5.24 6. II 10.89 5. 34 



CaO 8.36 8.13 8.66 7.50 10.20 



NaoO 2.75 3.09 3.81 3.02 2.47 



K2O ,81 1.20 .86 .56 .95 



H2O— 43 .48 .73 .65 .48 



Ho O — .... .18 .12 .12 .10 .12 



CO2 .12 .35 .07 .23 .37 



!^i0.2 1.20 3.37 2.54 1. 18 S.26 



P2O5 .20 .57 .33 .14 .28 



S .07 .14 .11 .06 .26 



MnO .16 .24 .26 .22 .17 



NiO.CoO... .02 .02 .03 .02 ....'.. 



V2O5 .02 



100.02 99.98 99-77 99.72 100.75 



1 Wall rock of titaniferous magnetite. Split Rock mine, Westport. Analysis by W. F. 

 Hillebrand. 



2 Woolen mill i mile west of Elizabethtown. Analysis by W. F. Hillebrand. See above 

 p. 40. 



3 Gneissoid gabbro, 2 miles south of Elizabethtown. Analysis by W. F. Hillebrand. 



4 Massive gabbro, same exposure as No. 3. Analysis by W. F. Hillebrand. 



5 Wall rock of titaniferous magnetite. Lincoln Pond. Analysis by George Sceiger. 



1 19th An. Rep't. 1899. pt III. p. 377-422. 



