46-(16) MINERAL PHYSIOLOGY. 



crystallize various ores and spars, and to produce artifi- 

 cially a greater number of the mineral species found in vein- 

 stones. The curious processes of selection and elimina- 

 tion by which so many of the rarer elements are gather- 

 ed from the great mass of the earth through which they 

 were originally distributed, would require for their dis- 

 cussion a more extended study than our present limits 

 permit, but Ave may remark that selective diffusion 

 and osmosis doubtless play an important part therein, 

 as they certainly do in many processes in the organic 

 world. 



The experiments in the chemist's laboratory, conduct- 

 ed at temperatures considerably above the boiling point 

 of water, enable us to produce many mineral species in a 

 short time, but we have evidence that similar results are 

 produced, though more slowly, at much lower tempera- 

 tures. The baths constructed by the Romans with brick 

 and mortar at various hot springs in France, less than 

 twenty centuries since, have within the last few years 

 been found to contain in the cavities of the masonry a 

 great number of crystallized mineral species identical 

 with those met with in mineral veins, all of which have 

 evidently been formed within that time by the action of 

 the mineral waters at temperatures considerably below 

 that of boiling. Again, in California and Nevada, ther- 

 mal waters still bring to the surface dissolved silica, 

 which they deposit in the fissures of the rocks, together 

 with sulphuret of mercury, pyrites and gold, thus giving 

 rise to veinstones closely related in composition to the 

 more ancient ones to be found in the rocks near by. The 

 great quartz vein of that region, known as the Comstock 

 lode, has been formed in times geologically very recent, 

 by the action of hot waters resembling those now flowing 

 in its neighborhood. 



To explain the origin of the various mineral waters 

 which have formed the veinstones, would involve a dis- 

 cussion of the whole doctrine of the terrestrial circula- 

 tion. It may be said in a few words that the rocks of 

 the earth's crust are more or less permeable to water, 

 which filters through porous beds or flows through joints 

 or fissures, carrying with it gases dissolved from the at- 

 mosphere, and the results both of organic and mineral 

 decay, very complex and variable in composition, taken 



