* Dissolving shells distil. l. 93. The lime-stone rocks have had their origin from shells formed beneath the sea, the softer strata gradually dissolving and filling up the interstices of the harder ones, afterwards when these accumulations of shells were elevated above the waters the upper strata became dissolved by the actions of the air and dews, and filled up the interstices beneath, producing solid rocks of different kinds from the coarse lime-stones to the finest marbles. When those lime-stones have been in such a situation that they could form perfect crystals they are called spars, some of which possess a double refraction, as observed by Sir Isaac Newton. When these crystals are jumbled together or mixed with some colouring impurities it is termed marble, if its texture be equable and firm; if its texture be coarse and porous yet hard, it is called lime-stone; if its texture be very loose and porous it is termed chalk. In some rocks the shells remain almost unchanged and only covered, or bedded with lime-stone, which seems to have been dissolved and sunk down amongst them. In others the softer shells and bones are dissolved, and only sharks teeth or harder echini have preserved their form inveloped in the chalk or lime-stone; in some marbles the solution has been compleat and no vestiges of shell appear, as in the white kind called statuary by the workmen. See addit. notes, No. XVI.


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