1050 General Notes. [ December, 
mineral and the feldspar of the rock, the latter supplying the 
former with the necessary aluminum required to build up the 
hornblende molecule. In addition to the two rocks mentioned, 
there are in the same region olivine-bronzite-gabbros, feldspathic 
peridotites and Iherzolites. In some of these rocks the feldspar 
has undergone a rather unusual alteration, viz., into scolecite. 
Other rocks, composed entirely of bronzite or hypersthene with 
or without diallage, are mentioned and briefly described. These 
olivine and pyroxenic rocks have given rise to much of the serpen- 
tine so generally found in their neighborhood. In the August 
number of the American Journal of Science, Mr. J. S. Diller’ has 
an article on the peridotite of Elliott county, Kentucky. This 
rock, according to the author, occurs in well-marked dykes cut- 
ting Carboniferous sandstones and shales. A microscopic €x- 
amination shows it to consist of olivine and pyrope, with a small 
amount of ilmenite as primary constituents, and serpentine, dolo- 
mite, magnetite and octahedrite as secondary minerals. The in- 
phibole, however, the fibrous mineral in the rim is biotite. F rom 
a comparison of the composition of the peridotite and the inter- 
sected sandstones and shales and the discovery of both endo- 
ation of the rocks collected there have established him firmly in 
the belief that the granitoid and the glassy rocks are of entirely 
distinct eruptions, which took place at two different periods re- 
mote from each other, and that in many cases minute differences 
of chemical composition have produced effects greater than m 
erate differences in the depths at which the roc í : 
moreover claims that a mere study of the slides and hand speci- 
mens is not sufficient to overthrow his own t 
sion of rocks in the vicinity of the Comstock lode. Profe 
sor R. D. Irving, of the United States Geological suney e PR 
article in the American Journal of Science, maintains % 
iron ores and the associated jaspery schists of the Lake upe 
1 Amer. Jour, Sci. XXXI, Aug., ’86, p. 122. : 
2 Cf. AMERICAN NATURALIST Notes, Feb., 1886, p. 161. 
ee Bulletin 6, California Academy of Sciences, p. 93- 
~ #Cf, AMERICAN NATURALIST Notes, Dec., 1885, p. 1216., ior region- 
_ 5 Origin of the ferruginous schists and iron ores of the Lake Superior 
er. Jour. Sci., XXXIL, Oct., ’86, p. 255. 
a eee 
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