SCIENCE. 



129 



these rocks as a whole, it is possible that thej- 

 can be divided into more than one species. 

 As the analj'ses stand, the rock is composed 

 of iron, either native or combined, with or 

 without varj-ing amounts of nickel, cobalt, 

 tin, copper, sulphur, titanum, phosphorus, 

 silica, graphite, etc. The specific gravity is 

 high. The presence of graphite shows that 

 it is not of organic origin in this case. 



Many of the so-called meteoric irons are 

 probably of terrestrial origin, and their envi- 

 ronment ought to be carefully studied. The 

 Wiedmanstattien figures are in some measure 

 paralleled by the leucoxene and cleavage 

 structure of titaniferous and magnetic iron in 

 diabases, etc. 



The name ' siderolite ' was formerly given 

 by Maskelyne to the species to whicli G-. Rose 

 had previously given the name ' pallasite ' ; 

 hence, since the latter has the prior right, it 

 is hoped that Maskelyne will allow the trans- 

 ference of the term ' siderolite ' as his own, to 

 this species, to which it most properlj' belongs, 

 since its individuals are emphaticall}' rocks of 

 iron. 



2. Pallasite. — This species is formed from 

 a series of rocks of lilte origin to the preceding ; 

 and the structure is that of a sponge- or semi- 

 spono'e-like mass of iron, either native or sec- 

 ondary, holding silicates. The iron has the 

 associations usual in siderolite ; and this as- 

 sociation holds good wherever the iron occurs 

 in meteorite.s, and probablj- on more careful 

 study will be found to hold good, to a great 

 exteut, in terrestrial rocks. The silicates are 

 principally olivine alone, or in association with 

 enstatite and diallage. More rarely feldspar 

 and other silicates occur. There are but two 

 or three complete analj-ses of the pallasites 

 that can be regarded of value ; Joy's \_Amer. 

 journ. sc, 1864 (2) xxsvii. 243-248] being 

 the best yet made. The silica increases in 

 amount, up to some 30%, averaging about 

 20%, with variable quantities of magnesia, 

 rarely exceeding 24% ; while the remaining 

 constituents are chiefly iron and its associates. 

 Specific gravity less than in the siderolites. 



Under pallasite are classed the supposed me- 

 teorites of Atacama, Bitburg, Brahin, Breit- 

 enbach, Krasnojarsk, Potosi, Rittersgriiu, 

 Rogue River, Sierra de Chaco, Singhur, and 

 more doubtfully those of Haiuholz, Mejiel- 

 lones, and Lodran. Of terrestrial rocks under 

 the pallasites belong the olivine-maguetite 

 rocks of Cumberland, R.I., and Taberg, Swe- 

 den ; for which, as a varietal form, I would 

 propose the name ' cumberlandite '. It is 

 probable that many other pallasites will be 



found on careful investigation of the iron- 

 bearing rocks. Some schistose rocks (actino- 

 litic) are probably the result of the extreme 

 alteration of the cumberlandite. 



The Ainsa and Carlton meteorites from Tuc- 

 son have a fine sponge structure, and contain 

 numerous olivine ( ?) grains ; but, although 

 thej- approach the pallasites, the3- have been 

 classed with the siderolites. 



3. Peridotite. — This term, applied by Ros- 

 enbusch to the pre-tertiary terrestrial olivine 

 rocks, I would extend to all terrestrial rocks 

 and meteorites of a similar composition, — 

 including everj' thing from the pallasites to 

 the basalts. These rocks are composed prin- 

 cipally of silicates and iron ; the former pre- 

 ponderating, and the latter sometimes wanting. 

 The silicates are principallj' olivine, enstatite, 

 and diallage or augite, and sometimes feld- 

 spar. The iron is either native, or in the 

 form of pyrrhotite, magnetite, chromite, etc. 

 Silica and magnesia are more abundant, as a 

 rule, than in the pallasites, and less so than 

 in the basalts, while the iron is less than in 

 the former. The specific gravity is also in- 

 termediate between the two above-mentioned 

 species. 



If it is desired, similar varieties can be 

 pointed out in the meteoric peridotites as in 

 the terrestrial forms : as, for instance, dunite 

 (Chassignj'), olivine-enstatite rock (Iowa Co., 

 Knj-ahinya, Gopalpur, Lanc6, Tourinnes, Wa- 

 conda, Goalpara) , Iherzolite (Pultusk, Esther- 

 ville, New Concord, etc.). Also, if desired, 

 an olivine-enstatite-augite division can be made 

 (Tieschitz, Hungen, Grosnaja, etc.). 



While part of the meteoric peridotites are 

 entirely crystalline, e.g., Esthcrville, the great 

 majority' are not so, but chondritic in structure. 

 The chondritic structure I believe to be caused 

 b_y the rapid solidification and arrested crj-stal- 

 lization of the masses composed of minerals 

 naturallj' taking a more or less I'ounded form ; 

 and not from mechanical action, as has gener- 

 ally' been claimed. These choudrae show, as 

 a rule, a light or dark graj' finely fibrous or 

 fibrous-granular base and semi-base, answer- 

 ing to the globulitic base of the basalts or the 

 felt^' base of the andesites. This base has 

 heretofore beeu described as a flocculent 

 opaque-white material, a cloudy substance, the 

 comminuted material, the feldspathic material, 

 etc. Sometimes it is isotropic ; but more com- 

 monly it affects polarized light according to 

 the amount of olivine or enstatite granules 

 formed in it. When crj^stallization goes far 

 enough, these granules form by their union 

 the enstatite and olivine grains and crystals. 



