IV. "GNOMES! you then bade dissolving SHELLS distil
From the loose summits of each shatter'd hill,
95 To each fine pore and dark interstice flow,
And fill with liquid chalk the mass below.
Whence sparry forms in dusky caverns gleam
With borrow'd light, and twice refract the beam;
While in white beds congealing rocks beneath
100 Court the nice chissel, and desire to breathe.--


[Footnote: _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,