558 DEEP-SEA DEPOSITS. 



Many observers have catalogued the substances contained in atmos- 

 pheric dusts. We need not mention here the organic and organized 

 particles, among which, as Mr. Pasteur and his pupils have shown us, 

 microbes occupy such a preponderant i)lace. What interests us is that 

 the mineral grains are also prodigiously abundant. This mineral por- 

 tion consists principally in very minute debris of terrestrial rocks, 

 which, in spite of their extremely small dimensions, can be exactly 

 determined by the microscope — such as quartz, limestone, the volcanic 

 silicates, and oxide of iron, which are easily diagnosed. 



In the course of these microscopic examinations, minute substances 

 have been found differing- entirely by their spherical form from the 

 small fragments j^roduced by the crushing- of rocks. The substances 

 in question resemble exactly the hollow globules or vesicles of oxide 

 which the quick combustion of metallic iron gives for example, when the 

 old-fashioned tinder box is used or when a horse's shoe strikes sparks 

 from the pavement. It is legitimate, however, not to consider all these 

 globules as having an artificial origin. 



Two classes of considerations may be appealed to on this subject. 



First, it is demonstrated that lumps formed of metallic iron or 

 containing granules of that metal, reach us from celestial space and 

 undergo in the higher regions of the atmosphere an artificial combus- 

 tion. The latter fact is manifested by the long trains of smoke, often 

 persistent, which accompany the meteorites. They contain very prob- 

 ably globules analogous to those i:>roduced from horse-shoes on the 

 pavement. 



In several circumstances the enormous volume of the dust in question 

 has been ascertained from the clouds or trails which have accompanied 

 the fall of celestial bodies. By reason of the importance of the fact, 

 we will cite several examples. 



At the time of the fall of the holosiderite, or iron of Hraschina, near 

 Agram (May 26, 1731), there was perceived, after the explosion, a black 

 cloud which lasted, it is said, for three hours and a half after the fall. 



At the moment of tlie fall of the iron of Braunau, in Hungary, 

 which took place July 11, 1847, many persons, warned by two violent 

 reports, remarked a small black cloud which appeared horizontally, 

 with the accompaniment of violent reports; two globes of fire, which 

 issu.ed from the cloud, fell upon the ground. The cloud became gray 

 and then disappeared. 



The mass from which, on the 14th of May, 1803, chondritic meteorites 

 fell in the environs of Orgueil (Tarn et Garonne), gave forth a jet of 

 sparks; then left behind it a trail, which was at first luminous, and then 

 changed to a cloud, lasting from eight to ten minutes. 



Before the explosion of the meteorite to which we owe the aero- 

 lites which fell on the 9th of December, 1858, at Ausson and at Chirac, 

 near Montrejeau (Haute Garonne), a considerable jet of incandescent 

 gmoke was seen to escape from the uucleus, A cloud of whitisU 



