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These meteorites are exceedingly tough, so that it is difficult to 

 break them up ; this is due to the iron grains being partly connected 

 by fibres and folia. Still, the nickeliferous iron is present in detached 

 masses, or occurs sporadically in the stone. Hence these meteorites 

 belong to the great class of Sjioradosideres of Daubree. In this class 

 Daubree distinguishes three species : those containing much, little, or 

 but very little iron, so that it can only be recognized by a magnifier 

 or a microscope ; these species he designates as Poly-, Oligo-, and 

 Krypto-Sporadosideres. Accordingly, the Iowa County meteorites are 

 Oligo-Sporadosidi,res, that is, meteoric stones containing but little 

 plainly visible metallic iron, in detached grains. I find that these 

 stones contain seven per cent., by weight, of metallic iron. The spe- 

 cific gravity of these meteorites is, therefore, rather low, namely 3.57. 



The fracture is very rough and uneven, showing the lustrous 

 metallic iron, and also irregularly rounded spots of lighter gray to 

 white on the dark-gray ground. These rounded stony concretions 

 show very well on a ground surface of the stone; they have given rise 

 to the name Chondrites, introduced by G. Rose, for this class of me- 

 teorites. I find that the grains of lighter color contain less of iron sili- 

 cate, but otherwise are composed of the same minerals. 



These minerals are essentially two, namely, Olivine, which is solu- 

 ble in muriatic acid, and Pyroxene, which is not soluble in this acid. 



Besides, the stone contains some troilite, that is, iron sulphide. 

 The following table gives the mineralogical composition of the Iowa 

 County meteorites, according to a number of analyses : 



( Troilite 1.8 



Non-Magnetic < Olivine 52.9 



( Pyroxene. 44.9 



Magnetic Nickeliferous Iron. . . 7.5 



The olivine is the variety known as Hyalosiderite, which contains 

 two atoms of magnesium to each atom of iron. In the pyroxene of 

 these meteorites the same ratio of iron and magnesium obtains ; hence 

 this variety is Hypersthene. 



The following table gives the result of my analyses of the average 

 composition of the Iowa County meteorites : 



Soluble 54.7 



Insoluble 44.9 



