Apbil 15, 1910] 



SCIENCE 



599 



Mr. D. B. Sterrett presented a description of 

 peculiar boulder or toadstool-like erosion forms 

 occurring over the outcrop of a batliolith of coarse 

 porphyritic granite in York County, S. C. Some of 

 these " toadstools " are ten to fifteen feet high and 

 of similar thickness, and are still firmly attached 

 to the underlying granite mass by stems which 

 may be only one third as thick as the boulder. 

 The granite also outcrops as floors or bosses sim- 

 ilar to the occurrences at some of the quarries of 

 the Piedmont region. 



Regular Program 

 Some Mineral Relations from the Laboratory 



View-point: Akthue L. Dat. 



The fundamental problems of rock formation, 

 to which petrologists are now giving serious atten- 

 tion, require much more than a perfunctory appli- 

 cation of chemistry and physics. The present 

 relations of the minerals in the rocks are ac- 

 cessible to the microscope under convenient con- 

 ditions of observation, but their development from 

 the fluid magma requires a laboratory study of 

 the rock-forming minerals over a wide range of 

 measured conditions of pressure, temperature and 

 concentration. It is of the first importance that 

 the evidence gathered be quantitative and perti- 

 nent to the problem. 



Recent laboratory studies have developed the 

 fact that the temperature of crystallization of a 

 mineral from its own liquid or from a mixture is 

 generally variable and therefore untrustworthy in 

 revealing the conditions of equilibrium during 

 formation. Melting point measurements therefore 

 furnish better determinations of the temperature 

 of change of state. It is also necessary that the 

 methods chosen for such determination be appro- 

 priate to the substance under investigation, for 

 minerals are characterized by strong individuality 

 of behavior near the melting temperature, which 

 makes it impossible to apply a single property 

 (the appearance of fluidity, for example) to de- 

 termine when melting occurs in all substances. 

 The lack of sharpness in melting point determina- 

 tions is partly the result of carelessness in prepa- 

 ration of experimental conditions, partly of mol- 

 ecular inertia or viscosity which prevents any 

 rapid rearrangement of the molecules of the liquid, 

 and occasionally (in isomorphous mixtures) to 

 changing composition during the change of state. 

 The first of these can be eliminated; the second is 

 characteristic of certain minerals and therefore a 

 matter of record; the third is an essential feature 



of the problem requiring special study. The 

 earlier melting point data ofi'er little evidence 

 upon which to discriminate between these cases. 

 An important factor in rock formation is brought 

 to light by the second of the properties noted 

 above, of which an excellent illustration is found 

 in quartz. In the laboratory, the fusion of pure 

 silica docs not occur below 1600° and is accom- 

 panied by conditions of extreme viscosity. In 

 nature, vein quartz appears to have crystallized 

 below 800° and to have been very fiuid at that 

 temperature. This suggests that volatile ingredi- 

 ents must have assisted in the formation of nat- 

 ural quartz of which only traces now remain, and 

 its proper laboratory study must include these 

 ingredients. The situation also reveals what is 

 perhaps the chief function of pressure in rock 

 formation— namely, in holding the volatile in- 

 gredients in solution. 

 Igneous Metamorphism: A. C. Spencer. 

 Platinum in Southeastern Nevada: Howland C. 



Bancroft. 



At the Key West and Great Eastern prospects 

 in the Copper King Mining District of Clark 

 County, Nev., platinum occurs in peridotite dikes 

 of the enstatite-miea-picrite variety. The proper- 

 ties are situated in the rough foothills of the 

 Virgin Range at an elevation of approximately 

 3,600 feet and are eight or nine miles from the 

 Virgin River. 



The rocks in the immediate vicinity are gneisses, 

 probably of pre-Cambrian age, and are intruded 

 along the planes of schistosity by basic dikes 

 which contain, in addition to platinum, primary 

 pyrrhotite (probably nickeliferous) , magnetite, 

 chalcopyrite and pyrite. Besides the peridotite 

 dikes there is also present a typical hornblendite 

 dike which shows upon analysis a trace of plat- 

 inum. Alteration and concentration of the sul- 

 phides in the rock by solutions seems to increase 

 the percentage of platinum and nickel, one an- 

 alysis showing the presence of .55 of an ounce of 

 platinum to the ton and over 5 per cent, nickel. 

 The dikes as exposed upon the surface vary in 

 width from 10 to 50 feet and are about 100 feet 

 long. 



One car-load of ore has been shipped from the 

 Key West workings. If these properties were near 

 a railroad, or if the ore could be treated on the 

 ground, it is quite probable that they would be 

 able to produce bullion. Under present conditions, 

 however, working expenses would be very high. 

 Edson S. Bastin, 



Secretary 



