So Dr. Mac Culloch on the Origin, Materials, 



sage to oil, but even permit sulphuric acid to follow, and to pre- 

 cipitate the charcoal within the pores of the stone. 



That the water in stones is actually saturated with earths, and 

 probably with silica or lime, appears to be also proved, by 

 certain appearances which take place on breaking find drying 

 some of these. In marbles raised very wet from the quarry, a 

 tvhitish dusty surface soon follows, from the deposition of the 

 carbonate of lime ; and it is probable, that a sitnilar cause will 

 dccount for that gray tarnish which is produced in pitchstones, 

 within a very few hours after the specimens are broken from the 

 rock; during which process of drying, they also become far itiord 

 Compact, or less tender. Thus the objection in question falls to 

 the ground ; were it even necessary that the process of consoli- 

 dation should be reserved for that time at which the whole stra- 

 tum was completed. 



Of the different Rocks, and the Modes of their Consolidation. 



Now although a large portion of the strata of the globe mky 

 have been formed by this last process of aqueous solution, and 

 a considerable portion, at least, of the secondary ones probably 

 btve their origin or consolidation to this cause, there are many 

 Strata, particularly in the primary or older series, to which it 

 is impossible to apply it, so as to explain all the appearances 

 #hich they present. It '\H^ill here be convenient to point out in 

 succession, those which may have been consolidated merely from 

 water, ending with those which will not admit of that explana- 

 tion; and it will remain to inquire, whether the phenomena 

 cannot be explained by the successive agency of both the caus6S 

 #hich have been examined. It will also b6 seen, that in otte iri- 

 stance, at least, among these ancient strata, either cause sepa- 

 rately might have produced the effects visible. 



There is nothing in the character of quartz rock, as far as I 



have examined it, to prevent it from having been consolidated 



to its present condition from the long continued application of an 



aqueous solution of silica. But that it was deposited from water 



riginally in the state of sand and gravel, is rendered evident 



