666 THE POPULAR SCIENCE MONTHLY. 



retarded them and made the progress very slow down to the mid- 

 dle of the present century. 



At the beginning of the cycle there existed the two opposing 

 geological camps, the one attributing everything to fire, the other 

 all to water ; after long years of wrangling their union was accom- 

 plished through the efforts of Lyell and his followers. In addition 

 to this, the accumulating observations overthrew two old ideas 

 namely, that a mineral can only originate in one way characteristic 

 to it, and a single homogeneous magma can give rise to only one 

 mineral. It was found that a mineral may originate under differ- 

 ent conditions which are determinable, and that the homogeneous 

 magma may at the same time give rise to different minerals. The 

 various mineralogists appeared to take pleasure in throwing an 

 envelope of mystery around the origin of minerals, and they were 

 regarded, even by Zirkel, as the work of a kind of vital force. 



Practical difficulties deterred the progress of the study; the 

 crystals formed were sometimes imperfect and usually micro- 

 scopic. So it was almost impossible to study them before the de- 

 velopment of mineralogical micrography and the advent of the 

 mineralogical microscope. Then it was found that these minute 

 imperfect crystals were of more value and led to greater results 

 than the more beautiful cabinet specimens, for they settled the 

 problems of origin. Natural crystals were found to contain small 

 inclusions which are indices to the origin. If these are vitreous, 

 then the origin is vitreous, and the action of volatile agents is 

 wholly excluded ; if these be aqueous, the intervention of water is 

 indisputable. In certain minerals as quartz, beryl, topaz liquid 

 carbonic acid appears as an inclusion, giving evidence of their 

 formation under great pressures. 



From this brief survey we see the strong prejudices of the an- 

 cients are disappearing ; observation and the processes of investi- 

 gation have acquired a remarkable precision ; materials and ap- 

 paratus in the laboratories have been perfected to a remarkable 

 degree. 



Under the head of artificial minerals we exclude those acci- 

 dentally formed in the industrial works, as graphite on the walls 

 of iron furnaces, for such do not answer the question of their 

 origin, since the reagents and conditions remain unknown. Nev- 

 ertheless, the recorded observations of such products have aided 

 reproduction in the laboratory, and it is of interest that these ob- 

 servations have been noted especially by German workers, while 

 the home of active laboratory investigation is in France. The 

 Germans collected the facts, while the French co-ordinated them, 

 forming hypotheses and then experimenting to prove them. The 

 Russians followed with almost equal success ; also much impor- 

 tant work has been done in the laboratory by the Germans. 



