T. S. Hunt on Lithology. 251 
voleanic 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 tempera- 
ture requisite to expand the liquid so as to fill the fluid-cavities, 
provided they were formed under a pressure not greater than 
the elastic force of the vapor. This of course represents the 
lowest temperature at which the consolidation could have taken 
n this connection Mr. Sorby remarks that from Mr. Robert 
Hunt's observations on the mean increase of temperature in the 
incumbent strata;” and he concludes that wit regard to rocks 
and minerals formed at high temperatures, we have “at one end 
of the chain erupted lavas, indicating as gee and complete 
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