the same manner, though usually they are lefs perfectly chrystallized.

All forts of calcareous pars owe their origin to a fimilar cause.

While these natural ftalactites are of a small fize, they will continue to be regularly formed, and retain the figure of icicles ;because the water, as it oozes out, will be fufficient to furround the whole of the pap, and augment.it equally on every fide. But, in time, these will become fo large, as to cause the water flow down only on one fide, after which the figure will become distorted and irregular. Two or more will fometimes unite into one; and, in the course of ages, an infinite diversity of fantastic forms will gradually be produced, which may exhibit, on many occafions, figures of stupenduous magnificence.

$ 11.

The operations of nature are fo fimple, that, when we once get a glimpíe of the manner in which they are effected in one inftance, it is eafy to extend our observations in a fatisfactory manner to others of a fimilar nature. When we once perceive the manner in which calcareous ftalactites are formed, it is easy to comprehend the way in which more regular ftrata of calcareous fubftances have been produced. The fame cavern that produces the one will always afford examples of the other.

The drop of lime-water that falls from the roof of the cavern, although it has loft fome of the calcareous matter with which it was impregnated, ftill retains a part. When it reaches the ground, it either remains ftagnant fo as to form a pool, or flows over a fmooth

a fmooth furface. In either of thefe cafes, it will be allowed time to abforb fome more of its air; and a part, or the whole, of the calcareous earth will be rendered mild, and remain in a firm chryftallized folid cake of marble.

If the ftream is confiderable, the fheet of calcareous matter may be extended to a great difiance, thinly fpread over a large declivity, as the water flows in its course,-till at laft the whole cavity may be filled with a regular ftratum of lime-ftone-or marble.

In this manner, within the memory of man, have huge rocks of marble been formed near Matlock in Derbyshire,

which furnish matter of aftonishment to thofe numerous travellers who flock to fee this uncommon phaenomenon.-It is feldom that nature's operations are fo rapid as in this inftance. But there is no room to doubt, that all the ftrata of calcareous matter in the

world

1

world have been formed by a process exactly fimilar to this.

When the drops are fmaller, fo as not to be fufficient to form a large ftream, but ftill to flow over a small part of the furface, irregular fwelling cakes of lime-ftone are produced. When smaller ftill, they rise up into high prominences, with roundish heads,fometimes resembling collyflower, and fometimes brocoly heads.

If a current of air haftily promotes the evaporation of the water, the chryftallization will be less perfect. But enough has already been faid to illuftrate the fubject I have undertaken.

I now return from the operations of nature to those of art.

§ 12.

§ 12.

any

If flaked lime be expofed to the air for length of time, in the form of a dry powder, it abforbs the fixed air alfo in this ftate,in a fhort time lofes all its qualities as a quick-lime, and, chemically confidered, differs in no respect from the ftone of which it was compofed.

If no more water has been added at flaking than was barely fufficient to make it fall, and, if it be kept dry ever afterwards, or mixed with any dry powder, it does not harden as it absorbs its air, but remains in a powdery ftate, to all appearance in no refpect differing from quick-lime.

But, if a larger proportion of water has been added than was neceffary for flaking the lime,-in proportion as it abforbs its air and becomes mild, it concretes into a cohe