;o8 



NATURE 



[Jan. 30, 1890 



■stituents were originally at such a high temperature that they 

 were in a state of vapour, like that in which many now occur in 

 the atmosphere of the sun, as proved by the black lines in the 

 solar spectrum." We may, in fact, look upon them as being to 

 planets what the minute drops of water in the clouds are to aa 

 ocean. He has shown that possibly, after the condensation of 

 the vapour, they collected. into larger masses, which have been 

 subsequently changed by metamorphic action, broken up by 

 mutual impact, and again collected and solidified, the meteoric 

 irons possibly being those portions of the metallic constituents 

 which were separated from the rest by fusion when the meta- 

 morphosis was carried to the extreme point. 



In this manner the subsequent heating, or any number of 

 subsequent heatings, are explained. 



Iron Meteorites not fused in falling. ^ 



A question of no slight interest in regard to the changes 

 which meteoric irons undergo during their passage through the 

 atmosphere is whether their surface becomes fused. Ffom his 

 study of the Charlotte meteorite, Dr. Smith is inclined to answer 

 it in the negative. The fact of the delicate reticulated surface 

 having been preserved is a proof that the heat, instead of having 

 been raised to a high temperature, has quickly been conducted 

 away into the mass of metal. Had fusion of the superficial 

 layer taken place, the meteorite would have been coated with 

 ■molten oxide. 



Veins. 



Now and again we come across meteorites which have veins, 

 like terrestrial rock-veins, running right through them. Prof. 

 Maskelyne's description of them is as follows : — " 



" Just as in a mine one may meet with a fissure that, once 

 dividing the 'country,' but subsequently filled by rocky 

 matter, cuts across the course of a mineral vein which itself was 

 originally formed in a similar way ; and just as such a cross 

 fissure, thus intersecting with the original metalliferous vein, 

 often gives us evidence of a heave, i.e. that one side of the new 

 fissure has slid upwards or downwards along the other, so an 

 exactly similar thing is met with in meteorites, and is admirably 

 ■seen in the microscopic sections of them." 



Faults and throws are both represented in meteorites. In that 

 of Aumieres there is a throw of several centimetres indicated, 

 and faults intersect. These faults are accompanied by heat due 

 to the friction of the surfaces, and in the case of gray stony 

 meteorites the faults are black like the crust. ^ (The black veins 

 are physically connected with the crust, and are supposed to 

 have the same origin, the melted material having filled up the 

 •fissures. ) 



On examining such meteorites as Chateau-Renard, Pultusk, 

 and Alessandria, it is found that some of the spherules even are 

 broken in half and the halves separated from each other by a 

 vein of meteoric iron or troilite, and in some cases by a black 

 fused substance, like the crust of a meteorite. 



The Presence of Sulphides. 



The presence of sulphides, which must have been formed when 

 Tjoth water and free oxygen were absent, shows a distinctly non- 

 terrestrial condition, as, indeed, does also the presence of small 

 particles of iron. On this point Dr. Flight rema'ks : * "If the 

 conditions necessary for the formation of pure calcium sulphide 

 be borne in mind, the evidence imported into this inquiry by 

 the Bustee aerolite seems further to point to the presence of a 

 -reducing agent during the formation of its constituent materials." 



Sorby's General Conclusions. 

 We have before referred to Sorby's microscopical examination 

 •of meteorites. In 1865 he stated the general conclusions he 

 Jiad arrived at as follows. It will be seen how remarkable the 

 agree.uent is between him and Keichenbach. 



"As shown in my paper in the Proceedings of the Royal 

 Society (xiii. 333), there is good proof of the material of 

 meteorites having been to some extent fused, and in the state of 

 minute detached particles. I had also met with facts which 

 seemed to show that some portions had condensed from a state 

 of vapour ; and expected that it would be requisite to adopt a 

 modified nebular hypothesis, but hesitated until I had obtained 

 more satisfactory evidence. The character of the constituent 



' Quoted from the " Report on Observations of Luminous Meteors during 

 the year 1874-75," p. 247. '= Nature, vol. xii. p. 505. 



2 Flight, toe. cit., p. Ill 



•* Loc. cit.., p. 119. 



particles of meteorites and their general microscopical structure 

 differ so much from what is seen in terrestrial volcanic rocks, that 

 it appears to me extremely improbable that they were ever por- 

 tions of the moon, or of a planet, which differed from a large 

 meteorite in having been the seat of a more or less modified 

 volcanic action. A most careful study of their microscopical 

 structure leads me to conclude that their constituents were 

 originally at such a high temperature that they were in a state of 

 vapour, like that in which many now occur in the atmosphere of 

 the sun, as proved by the black lines in the solar spectrum. On 

 cooling, this vapour condensed into a sort of cometary cloud, 

 formed of small crystals and minute drops of melted stony matter, 

 which afterwards became more or less devitrified and crystalline. 

 This cloud was in a state of great commotion, and the particles 

 moving with great velocity were often broken by collision. 

 After collecting together to form larger masses, heat, generated 

 by mutual impact, or that existing in other parts of space through 

 which they moved, gave rise to a variable amount of meta- 

 morphism.- In some few cases, when the whole mass was fused, 

 all evidence of a previous history has been obliterated ; and on 

 solidification a structure has been produced quite similar to that 

 of terrestrial volcanic rocks. Such metamorphosed or fused 

 masses were sometimes more or less completely broken up by 

 violent collision, and the fragments again collected together and 

 solidified. Whilst these changes were taking place, various 

 metallic compounds of iron were so introduced as to indicate that 

 they still existed in free space in the state of vapour, and con- 

 densed amongst the previously formed particles of the meteorite;!. 

 At all events the relative amount of the metallic constituents 

 appears to have increased with the lapse of time, and they often 

 crystallized under conditions differing entirely from those which 

 occurred when mixed metallic and stony materials were meta- 

 morphosed, or solidified from a state of igneous fusion in such 

 small masses that the force of gravitation was too weak to 

 separate the constituents, although they differ so much in specific 

 gravity. (Report of British Association, 1864.) Possibly, how- 

 ever, some meteoric irons have been produced in this manner 

 by the occurrence of such a separation. The hydro carbons with 

 which some few meteorites are impregnated may have condensed 

 from a stale of vapour at a relatively late period. 



" I therefore conclude provisionally that meteorites are records 

 of the existence in planetary space of physical conditions more 

 or less similar to those now confined to the immediate neigh- 

 bourhood of the sun, at a period indefinitely more remote than 

 that of the occurrence of any of the facts revealed to us by the 

 study of geology — at a period which might in fact be called 

 pre-tcrrestrial." 



Are Meteorites merely Modern Phenomena ? 



It has often been a subject of remark that in spite of the very 

 considerable number of undoubted meteorites now in various 

 collections, we scarcely have traces of any which suggest like 

 falls in any of the geological periods preceding the present one. 



The iron found by Prof. Nordenskiold at Ovifac, Western 

 Greenland, was at first thought to be meteoric iron of Miocene 

 age, but after an analysis of the basalt or lava rocks of Assuk, 

 Disco Island, a part of the same basaltic range in Greenland, only 

 100 miles from the spot where Prof Nordenskiold's discovery was 

 made, it was held by most authorities to be no other than the 

 metallic nickel-iron which is, though extremely rarely, a native 

 product in some terrestrial rocks. Other explorers besides Prof. 

 Nordenskiold have brought back specimens of this iron, and 

 Dr. Lawrence Smith has stated, not only that the nickel-iron of 

 Ovifac is without doubt of terrestrial origin, but that the specimens 

 brought back by the other explorers resembles the Ovifac and 

 each other remarkably, while they differ from meteoric iron by 

 the large proportion of combined carbon in their composition. 



Again, in Nature, vol. xxxv. p. 36, we have a description of 

 another meteorite supposed to be a fossil one, found in a block 

 of Tertiary coal. It was said to belong to the group of meteoric 

 irons, and was taken from a block of coal about to be used in a 

 manufactory of Lower Austria. On its examination by various 

 specialists, different origins were assigned to it. Some believed 

 it to be meteoric, others an artificial production, and others 

 again thought it was a meteorite modified by the hand of man. 

 After a careful examination Dr. Gurlt came to the conclusion 

 that there was no ground for believing in the intervention of 

 human agency. The mass was almost a cube, two opposite faces 

 being rounded, and the four others being made smaller by these 

 roundings. A deep incision ran all through the cube. The 



