i66 Cincinnati Society of Natural History. 



substances when fused and slowly cooled, form crystals; as, 

 gold, silver, copper, antimony, and sulphur. It was found 

 when gypsum was fused and cooled, anhydride was the re- 

 sult. The temperatures required for the fusion are often so 

 great that certain gases, as fluorine, nitrogen, and others, are 

 used to aid in lowering the temperature, as in the case of 

 scheelite and zinc-blende. 



By the use of certain known solids, as fluxes, great assist- 

 ance was given. Ebelmen, by use of borax, formed crystals 

 of corundum. G. Rose, by means of certain salts of phos- 

 phorus, united with the oxides of silica, titanium, and iron, 

 formed tridymite, anatase, hematite. Bourgeois, likewise, 

 formed calcite, witherite, and strontianite, through a fusion 

 of the carbonates of the bases, with sodium and potassium 

 chlorides. Berthier formed, by same process, olivine and 

 some of the pyroxenes. In this connection may be men- 

 tioned the experiment of Sir James Hall, in which he fused a 

 crystalline rock (ophite) to a glass ; after this had cooled he 

 re-fused the glass, and by slow cooling formed again the 

 crystalline rock. By this means he proved that very high 

 temperatures were acting in the formation of the volcanic 

 rocks. 



The next division of the changes is that by divitiificaiiov. 

 It was early observed that certain glasses, long exposed, 

 showed a tendenc}' to crystallization. This was first observed 

 by Reaumer in 1727, and was further iiive.^tigattd h\ Hall in 

 1790. Leibnitz, finding that vitreous rocks were as.'^ociattd 

 with crystalline ones of same composition, as obsidian and 

 trachyte, concluded that the latter was derived frc m the 

 former by this peculiar property called devitrification, so he 

 concluded that "glass was the base of rocks." 



The most complete studies on this subject were made by 

 Fremy in his experiments on basalt. He heated a number of 

 specimens for eight days and found a change of color and the 

 formation of white feldspar crystals in a crystalline ground 

 mass. Four of these specimens were subjected to less and 

 less heat, and as a result it was found that the higher the 

 temperature the smaller were the bubbles. By similar means, 

 refractory clay, heated, showed crystals of sillimanite. Appert, 

 in 1890, observed that in soda and calcium glasses, quartz in 



