458 



stantly be formed in the compressed parts in accordance with the 

 fundamental principle of the explanation which I have propounded 

 the lowering, namely, of the freezing or melting point by pressure, 

 and the fact that ice cannot exist at cent, under a pressure exceed- 

 ing that of the atmosphere. I would also wish to make it distinctly 

 understood that no part of the ice, even if supposed at the outset to 

 be solid or free from porosity, can resist being permeated by the 

 water squeezed against it from such parts as may be directly sub- 

 jected to the pressure, because the very fact of that water being 

 forced against any portions of the ice supposed to be solid will 

 instantly subject them to pressure, and so will cause melting to set 

 in throughout their substance, thereby reducing them immediately 

 to the porous condition. 



Thus it is a matter of indifference as to whether we commence 

 with the supposition of a mass of porous or of solid ice. 



II. " On the part which the Silicates of the Alkalies may play 

 in the Metamorphism of Rocks." By T. STERRY HUNT, 

 Esq., of the Geological Survey of Canada. Communicated 

 by THOMAS GRAHAM, Esq., F.R.S., Master of the Mint. 

 Received March 30, 1857. 



In my last communication to the Royal Society on the Meta- 

 morphic Silurian Strata of Canada, I endeavoured to show, from the 

 results of analyses of the altered and unaltered rocks, that it is the 

 reaction between the siliceous matters and the carbonates of lime, 

 magnesia, and iron of the sedimentary deposits, which has given rise 

 to the serpentines, talcs, pyroxenites, chlorites, and garnet rocks of 

 the formation. I then cited the observation of Bischof that silica, 

 even in the form of pulverized quartz, slowly decomposes these car- 

 bonates at a temperature of 212 F., with evolution of carbonic acid ; 

 the same author mentions that a solution of carbonate of soda has 

 the power of dissolving quartz under similar conditions*. Desiring 

 to verify these observations, I have since made the following experi- 

 ments. 



* Bischof s Chem. and Phys. Geology, Eng. Edition, vol. i. p. 7. 



