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minute bubble becomes smaller and smaller, until finally the liquid 

 fills the whole cavity, the bubble completely disappearing. Now 

 it is evident that these -little parcels of water must have been 

 enclosed within the quartz on its solidification, when the granite 

 was being formed deep beneath the surface, for all geological 

 evidence goes to show that granite is deep-seated in its formation ; 

 although of various ages, yet no other rock is ever found beneath 

 it. Therefore^ it is further evident that when first enclosed, the 

 water must have been in a highly heated condition, and unable to 

 attain the'state of vapour by reason of the great pressure to which 

 it was subject ;"so that we may regard the liquid, now contained 

 in the quartz, as part of the original mother-liquor, if I may use 

 the term, which, together with a heated condition of other 

 minerals, and great pressure, made up the conditions under which 

 the granite was formed. In the formation of the granite, the two 

 minerals mica and felspar were the first to crystallize, impressing 

 their form upon the semi-molten or semi-fluid quartz, which 

 solidifying last, wrapt up within itself large quantities of the highly 

 heated water, in the form of minute liquid parcels or cavities. 

 Subsequently, on cooling of the mass, removal of pressure, or both, 

 the water would cool ; but being closely sealed up in glassy 

 (quartzy) cavities or minute bottles, it could not escape in the 

 state of vapour any more than at the first, but in its cool condition 

 would occupy a slightly less space ; in other words the contraction 

 would leave a minute bubble or empty space (called, for 

 convenience sake, a vacuity), which vacuity you will see must have 

 a size proportionate (ist) to the size of the liquid parcel ; (2nd) to 

 the heat and pressure under which the fluid was originally confined. 

 Hence, if it be found that in a number of cases the relative size of 

 vacuities and liquid-cavities is the same, these relative dimensions 

 give us a clue to the amount of combined heat and pressure under 

 which the granite (or, to speak more accurately, the quartz of the 

 granite) was formed. Here, then, is an interesting problem ; but 

 at the outset it appears that to find out the exact amount of either 

 the heat or the pressure it is necessary to know that of one of 

 these elements ; thus, if we knew the pressure, and observed the 



