18 THE CANADIAN NATURALIST. [Feb. 



both of granites and crystalline schists contains great numbers 

 of small cavities partially filled with water, or with concentrated 

 aqueous solutions of chlorids and sulphates of potassium, sodium, 

 calcium, and magnesium, sometimes with free hydrochloric acid. 

 Similar fluid-cavities were found by him in most crystals 

 artificially formed in aqueous solutions; and were also observed in 

 the minerals from the limestones of Vesuvius, where they occur 

 in nepheline, idociase, hornblende, and feldspar ; the liquid in the 

 latter crystals containing, besides chlorids and sulphates, alkaline 

 carbonates. Mr. Sorby has also described the cavities filled with 

 vitreous and with stony matters which he has observed in quartz, 

 in the feldspar of pitchstones, in augite, leucite, and nepheline ; 

 and which are sometimes found associated with fluid-cavities in the 

 same mineral. As these fluid-cavities enclosed the liquid at an ele- 

 vated temperature, its subsequent cooling has produced a partial 

 vacuum, which is again filled on heating the crystal ; so that the 

 temperature of the crystals at the time of their formation may be 

 approximatively determined. Mr. Sorby concludes that every 

 peculiarity in the structure of the quartz of the veins in Corn- 

 wall, " may be most completely explained by supposing that this 

 mineral was deposited from water holding various salts and acids 

 in solution, at temperatures varying from 200'^ C. to a dull 

 red heat visible in the dark" (about 340° C). At this highest 

 temperature he conceives that other minerals, such as mica, feldspar, 

 and tinstone were deposited ; the latter mineral containing numerous 

 small fluid-cavities. In like manner, he deduces from the fluid- 

 cavities in the Vesuvian minerals] ust noticed, a temperature of from 

 360° to 380° C. The presence at the same time of bubbles or vapoi- 

 cavities, and of glass and stone cavities in these crystals shows 

 them to have been formed " at a dull red heat under a pressure 

 equal to several thousand feet of rock, when water containing a 

 large quantity of alkaline salts in solution was present, along with 

 melted rock, and various gases and vapors. ^ ^ ^ * I therefore 

 think that we must conclude provisionally, that at a great depth 

 from the surface, at the foci of volcanic activity, liquid water is 

 present along with the melted rocks, and that it produces results 

 which would not otherwise occur." (Loc. cit., p. 483.) 



Mr. Sorby has, as we have just seen, determined the temperature 

 requisite to expand the liquid so as to fill the fluid-cavities, pro- 

 vided they were formed under a pressure not greater than the elas- 



