NOV. 4, HI21 abstracts: geology 441 



U. S. Coast and Geodetic Survey, the U. vS. Geological Survey, and the U. S. 

 Corps of Engineers are always given in geographic coordinates. \\Tien sur- 

 veys are made over small areas such as are occupied by cities and small coun- 

 ties, the use of plane coordinates is more convenient and the computations 

 are simplified. 



The tables in this publication enable the county or city surveyor w^ho wishes 

 to use the stations given in the above-mentioned government publications 

 for the control of his surveys, to convert quickly the geographic coordinates 

 given there into plane coordinates without the use of difficult formulas. The 

 development of the formulas used in the computation of the tables is given 

 in an appendix at the end of the book. W. F. R. 



INORGANIC CHEMISTRY.— r/i^ crystal structure of magnesium oxide. 

 Ralph W. G. Wyckoff. Amer. Journ. Sci. 1: 138-151. 1921. 



An attempt has been made, using Laue photographs and X-ray spectrum 

 measurements, to get a unique solution for the crystal structure of magnesium 

 oxide. If it possesses holohedral symmetry-, then the only simple structure 

 which is possible is the "sodium chloride arrangement." Certain cases of 

 grouping showing tetratohedral symmetry, and two more complicated holo- 

 hedral arrangements, each with thirty-two molecules associated with the 

 unit, are in agreement with the existing experiments. These other possi- 

 bilities, however, differ but slightly from the "sodium chloride arrangement," 

 and cannot be positively treated by the experimental facilities now available. 



R. W. G. W. 

 MINERALOGY. — Note on augite from Vesttvius and Etna. Henry S. 

 Washington and H. E. Merwin. Amer. Journ. Sci. 1: 20-30. 1921. 



The paper includes a description and analysis of crystals of augite collected 

 at the bottom of the crater of Vesuvius in 1914. The chemical composition 

 of the cr>'stals is almost identical with that of pyroxenites of Monte Somma, 

 described by Lacroix. The relative merits of the gravitative-adjustment 

 and fraction al-cr}-stallization theories of certain forms of differentiation are 

 discussed. 



Crystals of augite from Monti Rossi, from the eruption of Etna in 1669 

 are also described, with a new analysis and optical determinations. No 

 good analyses of the augites of either Vesuvius or Etna are to be found in 

 the literature. Spallanzani (circa 1790) was the first to determine the relative 

 melting points of the feldspars and augite, and to measure their relative mag- 

 netic susceptibility; he is therefore to be regarded as the first experimental 

 geophysicist. The paper also gives a comparison of the chemical compositions 

 of various Italian augites with the lavas that contain them. H. S. W. 



GEOLOGY.— r/t^ Divide silver district, Nevada. Adolph Knopf. U. S 

 Geol. Survey Bull. 715-K. Pp. 24 (147-170). 1921. 



The Divide district, one of Nevada's newest silver camps, centers at Gold 

 Mountain, 5 miles south of Tonopah. The discovery of silver ore that started 

 the great activity at this camp was made late in 1917, wholly by chance. 

 A crosscut was being driven to cut a small gold vein that had been worked 

 higher on the slope of Gold Mountain intermittently since 1902, and before 

 it had been driven far enough to cut the gold vein it quite unexpectedly inter- 

 sected a rich silver-bearing lode. Further exploration indicated that a large 

 and valuable ore body had thus accidentally been discovered. 



The prevailing rock in the Divide district is the Fraction rhyolite breccia. 

 This is intruded by several stocks of the Oddie rhyolite and by a large mass 



