400 Rajinesque on Atmospheric Dust. 



It does not appear that it has any bad influence on men and 

 animals breathing it along with air, unless it should be accu- 

 mulated in a very intense degree. 



13. At Segesta, in Sicily, are to be seen the ruins of an 

 ancient temple ; the steps, which surround it on all sides be- 

 low 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 t» 

 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 eur rooms is 

 produced by the fragments of decomposed vestments, bed- 

 dings, 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. 



16. 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 con- 

 sideration by geologists, that the air still deposits a quantity 

 of dust, which must have been much greater in former pe- 

 riods. 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 ! 



