204 GRANITES AND GRANITIC VEIN-STONES. [XI. 



show these veins to have been deposited in fissures communi- 

 cating with the surface-waters of the liassic period. For a. 

 description of these veins by Mr. Charles Moore, see the Re- 

 port of the British Association for 1869, and Amer. Jour, of 

 Science (2), L. 365. Similar evidence is afforded by the exist- 

 ence of rounded pebbles imbedded in veins, as observed in 

 Bohemia and also in Cornwall, where numerous pebbles both 

 of slate and quartz were found at a depth of six hundred feet 

 in a lode, cemented by cassiterite and sulphuret of copper. (Ly- 

 ell, Student's Elements of Geology, p. 593.) Not less instruct- 

 ive in this connection are the observations of Mr. J. Arthur 

 Phillips, on the silicious vein-stones now in process of forma- 

 tion in open fissures in Nevada. (L. E. and D. Phil. Mag. (4), 

 XXXVI. 321, 422 ; Amer. Jour, of Science (2), XLVII. 138.) 

 We cannot doubt that the ancient, like these modern veins 

 have been channels for the discharge of subterranean mineral 

 waters ; and it would seem that while the deposition of the in- 

 crusting materials on the walls of the fissure is in part due to 

 cooling, and in part perhaps to infiltration, in some cases, of 

 precipitants from lateral sources, it is chiefly to be ascribed to 

 the reduction of solvent power consequent upon the diminu- 

 tion of pressure as the waters rise nearer to the surface.* This 

 conclusion, deducible from the researches of Sorby on the rela- 

 tion of pressure to solubility (ante, page 65), I have pointed 

 out in the Geological Magazine for February, 1868, p. 57. 

 See also Amer. Jour, of Science (2), L. 27. 



29. There is evidently a distinction to be drawn between 

 veins which have been open channels and the segregated 



* Of this a remarkable example was afforded in 1866 at Godericb, in Ontario, 

 where, in a boring at a depth of 1,000 feet, a bed of rock-salt was met, from 

 which for a time a saturated or rather supersaturated brine was obtained. 

 As an evidence of this, I saw a cube of pure salt, one fourth of an inch in 

 diameter, which had formed upon and around a projecting point of an iron 

 valve in the pump, above the surface of the ground. The liquid beneath a 

 pressure of 1,000 feet of brine, equal to about 1,200 feet of water, or thirty- 

 six atmospheres, having taken up more salt than it could hold at the ordinary 

 pressure, deposited a portion of it as it reached the surface, and actually ob- 

 structed thereby the action of the pump. After a few months of pumping, 

 however, the well ceased to afford a fully saturated brine. 



