406 Mr. J. A. Phillips on the Connexion of certain 



similar perhaps to those now existing at various points along 

 the eastern base of the Sierra Nevada, as, for example, at Steam- 

 boat Springs, Washoe"*. 



Daubree observes that veins can have been but very rarely 

 filled either by fusion or sublimation, but that, on the contrary, 

 the materials of which they are composed have been deposited 

 from solution in highly heated waters f. 



The late M. de Senarmont has shown that the principal mi- 

 nerals found in veins may be produced in a crystalline form by 

 the aid of water heated to temperatures varying from 130° to 

 300° Centigrade. Among the minerals which were thus ob- 

 tained may be enumerated quartz, spathose iron, the carbonates 

 of manganese and zinc, sulphate of baryta, sulphide of antimony, 

 mispickel, red silver ore, &c.J 



In the present state of our knowledge we are unable to ex- 

 plain all the various phenomena which have been observed in 

 connexion with the origin, composition, structure, and mineral 

 constitution of veins ; but a careful consideration of ascertained 

 facts would appear to lead to certain general conclusions, forming 

 a sort of skeleton map, of which the details remain to be filled in 

 by the aid of further research. 



First. Metalliferous lodes are more numerous and productive 

 in the vicinity of igneous rocks than elsewhere. 



Secondly. There is abundant evidence of volcanic eruptions 

 having taken place during all periods of geological time§. 



Thirdly. Solfatara action and thermal springs are often the 

 latest active evidences of volcanic disturbance. 



Lastly. Crystalline quartz, iron pyrites, sulphide of mercury, 

 and various other minerals are at the present time being depo- 

 sited by solfatara action, in veins possessing many of the charac- 

 teristics of ordinary lodes. 



* Report on the Property of the Empire Gold and Silver Mining Com- 

 pany, by Professor B. Silliman, Jim., and "W. P. Blake, p. 37. New 

 York : 1864. 



t Rapport sur les progres de la Geologie Experimental p. 63. Paris, 

 1867. 



X " Experiences sur la formation artificielle, par voie humide, de quelques 

 especes minerales qui ont pu se former dans les sources therm ales sous 

 Faction combinee de la chaleur et de la pression," Annates de Chimie et de 

 Physique, vol. xxviii. p. 693. " Experiences sur la formation de quelques 

 mineraux, par voie humide, dans les gites metalliferes concretionnes," 

 ibidem, vol. xxxii. (1851). 



§ Recent microscopical investigations have also shown that eruptive rocks 

 of very different geological ages completely agree in composition, texture, 

 and mode of occurrence. S. Allport, in a paper " On the Relative Ages 

 of Igneous Rocks," published in the Geological Magazine (October 1871), 

 says, " I have abundant evidence that melaphyres of undoubted Car- 

 boniferous age, and basalts of Tertiary age, have not only the same mineral 

 constitution, but also that both present the same structural variety." 



