THE NEW MINERALOGY. 667 



The practical side of a subject must always be considered, the 

 question of utility being a very important one. What claim has 

 this subject for attention and what has it accomplished ? It has 

 thrown light on the mode of the natural formation of minerals 

 and rocks. Thus even down to late time water was thought to 

 play an important part in the formation of a great number of 

 volcanic rocks and to be indispensable in the formation of the 

 great group of rocks termed basalt. Yet basalt and all the mod- 

 ern volcanic rocks have been formed by purely igneous fusion. 

 Again, certain minerals as chiastolite, garnet, staurolite, and a 

 large number of metamorphic minerals are always found impure 

 in Nature, and their exact composition was unknown until repro- 

 duced artificially. The majority of natural minerals are complex 

 combinations in which many bodies are introduced by isomor- 

 phous agency. Synthesis has furnished the theoretical types and 

 given forms which could be accurately measured and show the 

 true physical properties. 



Mineral synthesis determines the individuals belonging to a 

 family and distinguishes the true isomorphism of the series in 

 question. The artificial reproduction of the feldspar series 

 proved that the two members, alhite and anortJiite, were isomor- 

 phous and could be united in all proportions, some new forms be- 

 ing found which were unknown in Nature. Other mineral types 

 which are suggested by, but are absent in Nature have been 

 formed artificially, thus completing a mineral series, making the 

 limits of isomorphism more clear. This was accomplished by 

 Ebelmen in the spinel family, showing the relation of ferrites, 

 chromates, and aluminates to each other; also by Foque and 

 Levy in the feldspar family, who formed new feldspars with 

 bases of lithia, barytes, strontium, and lead. This work has also 

 been of great assistance to geology, a science which has been 

 encumbered by theories and hypotheses, where observation was 

 in very many cases insufficient to settle definitely the doubts. 

 Synthesis, when applied, enlarged the field of observation and 

 so often furnished definite solutions. Thus the origin of granite 

 was one of the great problems confronting geologists. The opin- 

 ion that it was purely igneous prevailed in the science for the 

 first part of our cycle, replacing the Neptunist or aqueous theory 

 of Werner, but the difficulties were increased a little later when, 

 by means of the microscope, it was found the quartz was con- 

 solidated after the other minerals ; this was against the idea 

 of a purely igneous fusion of the granite. The upholders of this 

 theory then argued for an extra fusion of the quartz analogous to 

 sulphur. Elie de Beaumont in 1849 modified the theory by ad- 

 mitting the intervention of water. For proof he called attention 

 to the number and frequency of the minerals sublimed on the pe- 



