64 



Cincinnati Society of Xatural History. 



Andesites were obtained in well crystallized specimens with the 

 normal structure, by fusing a mixture of four parts oligoclase and one 

 part augite. The mass was heated at a moderate temperature for 

 three days. The resulting microlites of oligoclase feldspar averaged 

 one-fourth millimetre long and 0.015 mm - broad. The augite was of 

 pale yellow color and in much smaller crystals than the oligoclase. 

 They were distributed irregularly among the feldspar microlites. 

 Octahedra of magnetite also were formed from the iron of the augite 

 employed. By the introduction of a slight excess of lime, microlites of 

 labradorite feldspar were formed. Augitic andesite was also formed 

 from a mixture of ten parts of oligoclase to one part of hornblende. 

 In this operation the hornblende is transformed into pyroxene. 



Basalts (see plate IV) were produced by heating a black homo- 

 geneous glass of the composition of an olivine rich basalt (6 parts 

 olivine, 2 parts of augite, 6 parts of labradorite.) The mixture was 

 kept at red heat for ninety-six hours. The resulting product, weigh- 

 ing fourteen grams, contained the minerals, olivine, picotite, labrado- 

 rite, augite, magnetite, and it was identical in every way with certain 

 natural basalts especially those of the Auvergne (France). This 

 artificial rock does not contain water, but microscopical examination 

 of natural basalts shows that the water is due to secondary alteration, 

 especially of olivine. These experiments definitely settle the question 

 of origin of basalts and show that they are of purely igneous origin. 



Nephelinites. A mixture of three parts nepheline to one and 

 three-tenths of augite fused and heated for two days yielded a crystal- 

 line product composed of microlites of nepheline and augite. When 

 the amount of augite is reduced, this mineral no longer appears in the 

 new rock. Thus ten parts of nepheline to one part of augite gives an 

 association of beautiful nepheline crystals, small octahedra of spinel, 

 and brown isotropic dodecahedra of melanite garnet. 



Leuate-tephrites . The chemical elements of the minerals com- 

 posing this rock (leucite, labradorite, augite) are fused to a homoge- 

 neous glass which is then heated for forty-eight hours at a white heat, 

 when the leucite elements are isolated and pass into a crystalline state. 

 A second heating is made for the same length of time at a cherry red 

 heat, below the fusing point of the feldspar, when the whole mass 

 becomes crystalline. 



Foque and Levy heated a mixture of silica, alumina, potash, 

 soda, magnesia, lime, iron oxide, representing one part of augite, 



