Mav 30, 1902.] 



SCIENCE. 



ment. The importance of such investigations 

 in their relations to soil-physics and scientific 

 agriculture was pointed out. 



Erratum. — In the report of the 551st meet- 

 ing (Science, May 2, 1902, page 710) the state- 

 ment regarding the consumption of liquid air 

 shotild read fifty gallons per week. 



Charles K. Wead, 



Secretary. 



THE SECTION OF GEOLOGY AND MINERALOGY OF 

 THE NEW YORK ACADEMY OF SCIENCES. 



The Section met on the 24:th of April, and 

 listened to the reading of two papers, abstracts 

 of which follow: 



Lea McI. Luquer, 'On the Determination 

 of the Relative Refractive Indices of Min- 

 erals in Rock Sections by the Becke Method.' 



In most schemes for the optical determina- 

 tion of minerals in rock sections, the birefri- 

 gence and resulting interference colors are 

 made the basis of the scheme of classification. 

 It is also desirable, however, to bring into con- 

 sideration an approximate knowledge of the 

 indices of refraction, and where the relative 

 differences in the indices of two adjoining- 

 minerals are required, the method devised by 

 Becke is found to be very convenient. This 

 method depends upon the principle of the 

 total reflection of light, and with proper ad- 

 justment of the microscope, which is to be 

 focused sharply on the dividing plane between 

 the two minerals, it is possible by slightly rais- 

 ing the objective, to observe a 'bright line' on 

 the side of the mineral having the higher in- 

 dex of refraction. 



The main precautions to be observed are 

 that the cone of incident light be small, the 

 sections very thin, the cementing material not 

 much lower in refractive index than either 

 of the minerals to be determined, and the 

 plane of contact clear and nearly vertical. 

 When the contact plane is much inclined, the 

 method cannot be applied. 



By this method very slight differences in 

 refraction can be distinguished; as for ex- 

 ample, between quartz sections cut parallel 

 and at right angles to the optic axis with the 

 difference 



f — (j = 0.009, f=l,553, u = 1.544 



Dr. Luquer's paper has been published in 

 the School of Mines Quarterly for January, 

 1902, pages 127-133. 



Austin r. Rogers, 'The Minerals of the 

 Joplin, Mo., Lead and Zinc District.' 



The minerals of the Joplin district include 

 sulphur, galena, sphalerite, covellite, greenock- 

 ite, wnrtzite, chalcopyrite, pyrite, marcasite, 

 quartz, cuprite, pyrolusite, limonite, calcite, 

 dolomite, smithsonite, cerussite, aurichalcite, 

 hydrozincite, malachite, azurite, calamine, 

 muscovite, chrysocolla, allophane, pyromor- 

 phite, barite, anglesite, leadhillite, caledonite, 

 linarite, gypsum, goslarite, chalcanthite, mel- 

 anterite, copiapite and bitumen, all of which 

 have been found by the writer. 



Lamellar twinning has been observed in 

 galena, the twinning planes being vicinal 

 tetragonal trisoctahedra. Covellite is found 

 replacing sphalerite. Wurtzite occurs in dis- 

 tinct hemimorphic crystals, the first instance 

 of the kind to be reported. Twin crystals of 

 marcasite are common, among them cyclic 

 fivelings. Quartz crystals are rare and small. 

 Calcite presents an interesting field for crys- 

 tallographic study, about twenty-four tjrpes 

 with a total of twenty-nine crystal forms hav- 

 ing been noted. Twinning according to all 

 of the four laws for calcite has been ob- 

 served. Some distinct crystals of aurichal- 

 cite confirm D'Archiardi's observations that 

 the mineral is monoclinic and that the axial 

 angle /3 is not 90°. Calamine occurs in doubly 

 terminated crystals which show their hemi- 

 morphic character plainly. Seamen's theory 

 as to the formation of calamine from 'tallow- 

 clay' is not in all eases applicable. The rare 

 copper-lead basic sulphates, caledonite and 

 linarite, occur at one mine at Galena, Kansas. 

 This mine also furnishes covellite, cuprite and 

 aurichalcite. 



The observed paragenesis generally follows 

 this order: dolomite, galena, sphalerite, chal- 

 copyrite, marcasite, pyrite, barite, calcite. 

 The total absence of certain silicates and the 

 rarity and small size of the quartz crystals 

 strongly preclude the theory that the lead and 

 zinc ores have been brought up from great 

 depths by hot waters. 



Attention was called to the coincidence in 



