134 EDSON S. BASTIN 



colorless zone showing a radial structure, and, especially where the olivine is in 

 contact with plagioclase, there is present always a second more or less regular 

 zone with similar structure. The latter is made up of an aggregate of green, rather 

 highly dichroic grains, all of which are hornblende. It seems as if these zones 

 were developed in consequence of a reaction between the plagioclase and the 

 olivine, the inner zone being formed at the cost of the latter, and the outer zone 

 at the cost of the former. The reaction zone is of particularly constant occurrence 

 between olivine and plagioclase, but between olivine and augite it is absent and 

 if augite penetrates in wedge-like form between olivine and plagioclase then the 

 two zones separate, the green remaining between the augite and the plagioclase 

 and the lighter zone between the olivine and the plagioclase, though both soon 

 wedge out. Neither by heating nor by acids were the zones notably affected. In 

 the much weathered portions of the rock the olivine inside the bright zone is 

 more or less completely altered to a dirty-green mass of serpentine."' 



THE FOLLOWING ANALYSIS OF THE ROCK IS BY 

 DR. W. F. HILLEBRAND^ 



SiOa 28.04 TiOa 20 



Al.O., 3.51 P2O5 04 



Fe.Oj ) ^, MnO 24 



FeO ( ""^'^^ SrO trace ? 



MgO 21.97 CO2 ■. 1. 01 



CaO ....1.78 Fe^Ss 21.53* 



Na,0 .28 NiS 945 



K,0 08 CoS 03S 



H,0+ 2.54 CuFeS. 1-03 



H,0- ' 1.48 Total 99.65 



Chlorite and calcite. — These minerals occur only in the more 



weathered portions of the rock in association with massive secondary 



hornblende and recrystallized ( ?) pyrrhotite. The chlorite belongs to 



the chlinocore variety and is mostly light green in color though a 



1 A. E. Tornebohm, "Ueber die wichtigeren Diabas und Gabbro-Gesteine Schwe- 

 dens," Neues Jahrhuch fur Mineralogie, 1877, pp. 382, 383. Translation by E. S. B. 



2 Laboratory of U. S. Geological Survey. 



One hundred grams of pyrrhotite were tested for platinum, but none was found. 



3 The iron was calculated as FeO. Some is present as Fe304, which would raise 

 the summation. The figure for the oxides of iron is only approximate because of the 

 impossibility of calculating the amount of pyrite or the exact composition of the other 

 sulphides. 



4 Includes some pyrite. 



s Occurs combined with or closely associated with pyrrhotite. 



The olivine grains contain so much magnetite in the form of inclusions that they 

 adhere strongly to a magnet. From microscopic examination it was estimated that 

 the magnetite formed about 17 per cent, by weight of the olivine or approximately 10 

 per cent, by weight of the whole rock. The iron belonging to the 14 . 95 per cent, of 

 FeO in the analysis (11 .63 per cent, of Fe) was redistributed on the basis of 10 per 

 cent, of Fe304, the total of the rock constituents thus being raised to 100.34 per cent. 



