EXPERIMENTS RELATIVE TO METEORITES, 339 



It is essential to have a correct nnderstanclinaf respecting this term scorificathn. 

 "We know that when a bath of inipnre castings is kept in fusion in contact with 

 the air, the iron is oxidized as well as certain bodies which arc associated with 

 it, of which silicinm is the most important. Tlie oxiciation gives rise to a fer- 

 ruginons silicate, wliich occupies the upper part of the metallic bath. This is a 

 true licpiid scoria; in cooling it will at Jirst become doughy, then solid; and in 

 the latter state will present a compact lithoidal crystalline structure ; one wholly 

 difi'erent, in a word, from the spongy and tufaceous substances to which we give 

 the name of volcanic scoricTe. Tlie former and metallurgic sense is that in which 

 we understand the scorification of the globe. 



As to the feldspathic rocks, many geologists consider that they have not been 

 produced simply by the dry way, as we have just shown has been probably the 

 case with the deep peridotic beds, but that they have been formed by the inter- 

 vention of particular agents, among others of water. However this may be, we 

 may here find, esj^ecially in the trachytes, the other extreme term of the series 

 of masses silicated in the general scorification. The opposition between these 

 two types, the most distinct and the best characterized, bears not only on the 

 niineralogical composition and the circumstances of crystallization, but also on 

 the density of these masses and their situation at depths necessarily very differ- 

 ent. Let it be remarked farther that this primitive scorification, extending 

 through a thickness so ^considerable, may, even at the existing epoch, i)resent, 

 according to the depth, masses in the three states of which we have been speak- 

 ing — solid, viscid, or liquid. * 



If metallic iron, quite habitual in meteorites, is wanting in terrestrial rocks, 

 tins difference may simply result from the circumstance that in our globe, where 

 the oxygen of the atmosphere is in excess, the oxidation may have been complete 

 and have left no metallic residue. When, however, we say that the terrestrial 

 masses contJiin no native iron it is evident that the question onl}' regards those 

 which eruptions render accessi'ble to our investigations ; masses which, in view 

 of the great dimensions of oin- planet, fomi but a sort of coating. There is 

 nothing to prove that below those aluminous masses which have furnished, in 

 Iceland, for example, lavas so analogous to the type of the meteorites of Juvinas, 

 that below our peridotic rocks to which the meteorite of Chassigny so closely 

 approximates, there do not exist Iherzolithic groups in which native iron begins 

 to aj:)pear; groupss that is to say, similar to the meteorites of the connnon typo; 

 then, going still lower, types more and more rich in iron, of which the metei)rites 

 offer us a series of increasing density, from those in which the quantity of iron 

 represents nearly half the weight of the rock to the massive iron itself. 



S«me facts might, perhaps, be brought to the support of these views. Thus, 

 platina, which its great density had probably placed, at the ])eginning, in profound 

 regicms, has, according to ]\I. Engelhardt, been found associated with native iron. 

 At all events, this last metal is allied to iron in a proportion wliich exceeds 10 

 per 100, and which suffices to render it strongly magnetic. It may be added 

 that if, in the Ural, platina has never been foinid in i)lace, it is oTten incrusted 

 witli chromate iron, and that it has even been met with still engaged in frag- 

 ments of serpentine.* By this association, therefore, this metal seems to convey 

 to us a new proof of the existence of maguesian rocks of the peridotic family, at 

 considerable depths. 



. ABSENCE m THE METEORITES OF STRATIFIED ROCTvS AXD OF GRANITE. 



Meteorites, so analogous to certain of our rocks, differ considerably from most 

 of those which fonn the terrestrial crust. 



* G. Rose, Reise nach Ural, t. ii, p. 390. Ee Play, Complcs Rendus deV Academic dcs 

 Sciences, 1846. 



