13. At Segesta, in Sicily, are to be seen the ruins of an ancient temple; the steps, which surround it on all sides below the pillars, are built on a rock, on the top of a hill detached from any other higher ground. Yet now all the steps and the base of the pillars are under the ground, which has accumulated from this dust and the decay of plants (not trees) to which it has afforded food. There are from five to eight feet from the rock to the surface of this new soil, which has chemically combined in a variety of hardness. This soil has arisen there in about 2000 years, notwithstanding the washings of rain. I quote this as a remarkable instance of the increase of soil by aerial deposits, among many which have fallen under my personal examination.
14. It is commonly believed that the dust of our rooms is produced by the fragments of decomposed vestments, beddings, furnitures, &c.; this cause increases it, and produces a different dust, which mixes with the atmospheric dust; but it is very far from producing it.
15. The dust of the open air is ascribed to that raised from roads and fields, by the pulverization of their surface; but this secondary and visible dust is only a consequence of the first. From whence could arise the dust observed by the means of the sunbeams in a dark corner, in winter, when the ground is frozen, or when it is wet and muddy, or at sea, or on the top of rocky mountains?
16. It is therefore a matter of fact, worth taking into consideration by geologists, that the air still deposits a quantity of dust, which must have been much greater in former periods. Just the same as the sea deposits still a quantity of earthy and saline particles dissolved in it, and which were superabundant at the period when the rocky strata were formed on its bottom. Water being more compact, deposits rocks. Air, which is less dense, deposits a pulverulent matter!
Art. XV. On the Effect of Vapour on Flame.
Art. XV. On the Effect of Vapour on Flame. By J. F. Dana, Chemical Assistant in Harvard University, and Lecturer on Chemistry and Pharmacy in Dartmouth College.
Cambridge, Mass. February 5, 1819.