THE GREENLAND BASALT. 203 



The descriptions are in part taken from the writings of others, in part from sections 

 belonging to the Whitney Lithological Collection, and in part from sections very kindly 

 sent me by Professor J. Lawrence Smith on his own motion. These sections were 

 the ones which had been nsed in the preparation of his "Meinoire sur le fer natif du 

 Groenlaud, et sur la dolerite qui le renferme." * 



One section, from Assuk, is composed of a gray groundmass, spriakled with little 

 rounded spots of a darker gray color, and porphyritically holding grains of feldspar, 

 magnetite, and iron. The groundmass is composed of predominating minute augite 

 crystals, in a matri.x of clear glass, containing miuute feldspars and elongated trichites, 

 similar to those seen in quartz and iron ores. The structural apjiearance is that of a 

 mass out of which the pyroxene material had mainly crystallized, leaving a colorless 

 glass, which in part had yielded feldspar crystals before congelation. The feldspar 

 crystals are, so far as observed, all plagioclase. A greenish secondary product not only 

 occurs in association with the iron ores, but also in detached masses and bordering 

 fissures. Its color varies from a bright grass-green to a dull dirty-green. Occasionally 

 it is found to be isotropic, but ofteuer to exhibit aggregate polarization, and it may be 

 classed under that convenient name for these variable secondary products — viridite. 

 Little, rounded pale-pinkish isotropic grains occur. They are apparently foreign, and 

 are considered to be garnet. A few large porphyritic crystals of feldspar were seen, 

 which are filled in the interior portion with inclusions — microlites, magnetite, glass, etc. 



The darker rounded masses observed in the section by tlie naked eye appear to 

 be of the same composition as the rest of the section, but with smaller crystals on 

 the whole, and with much finely-disseminated magnetite dust. 



This rock has been described by Steenstrup | and Toruebohm, J tlie former giving 

 a plate. Tornebolim regards the augitic mineral as enstatite, stating that it is optically 

 orthorliombic. In the section above described, the mineral is clearly monoclinic in its 

 optical characters, although it is perfectly possible that a rhombic pyroxene exists in 

 connection witli the augite. The iron ores occur in small rounded and irregular 

 grains, partly native iron, partly magnetite and pyrrhotite. L^sually a border of mag- 

 netite surrounds tlie metallic iron. 



The Ovifak basalt (dolerite) is described by Tornebohni as composed of plagioclase, 

 augite, olivine, titaniferous iron, and a glassy interstitial material. The augite is in 

 pale, clear-brown, almost colorless, irregular particles between tlie feldspars. Olivine is 

 found sparingly in little grains, which as a rule are fresh and unclianged. Bubble-bearing 

 glass inclusions occur in the augite, olivine, and feldspar. The titaniferous iron is in 

 elongated staff-like masses. The interstitial glassy masses appear only sparingly in 

 the angles, and as wedges between the above mentioned minerals. When fresh it 

 is of a fawn color and usually filled with microlites or dark spheres. Besides these 

 minerals there occur metallic iron, pyrrhotite, and a silicate rich in iron. This last 

 varies from a green to a dark-brown color. The metallic iron appears, in part, in 

 silver-white grains, often associated with magnetite, and sometimes with schreiber- 

 site. The pyrrhotite has in reflected light a yellowish-gray color, and is in larger 

 and smaller grains associated witli tlie other iron ores. 



The silicate rich in iron falls into two divisions : one a beautiful grass-green 

 color, isotropic, and allied to chloropb^ite ; the other a rusty-brown mass, sometimes 

 isotropic, and sometimes anisotropic, and here referred to hisingerite. § 



* Anu. Clilmie Phys., 1879 (5), svi. 452-505. f Miii. Mag., 1S77, i, U3-148. 



I Bihaug Kougl. Svenska "Vetens. Akad. Haudl., 1878, v., No. 10, pp. 18-21. § Ibid. pp. 1-22. 



