HANDBOOK OF THE METEORITE COLLECTIONS. 21 



plainly its secondary origin or introduction after the consolidation of 

 all other constituents except the sulphides. While its melting point 

 (about 1,500° C. or 2,732° F.) is somewhat lower than that of the as- 

 sociated silicates, the manner in which it frequently penetrates the 

 fractures of these constituents (see Admire pallasite) is so strikingly 

 like that of the native copper in the siliceous breccia of the Lake 

 Superior region as to suggest that it results not from a condition of 

 dry fusion, but rather from the reduction of some easily reducible 

 iron-rich compound like lawrencite. Such a reduction, as noted by 

 Nordenskiold ^ and others, must have taken place outside of our at- 

 mosphere and in an atmosphere deficient in oxygen. It may be noted, 

 incidentally, that the average amount of metallic iron in stony me- 

 teorites, as shown by Merrill, is 11.98 per cent, which is equivalent to 

 16.55 per cent of magnetite or 27.16 per cent of purely ferrous 

 lawrencite. 



The black crust coating the surface of the stony meteorites is, as 

 already noted, a more or less perfect glass, due to the fusion of the 

 various constituents from the heat generated during the passage of 

 the stone through the atmosphere. This, as shown in thin section 

 (see pi. 7, fig. 1), is rarely of more than a few millimeters in 

 thickness. It consists, as in the case of the Allegan stone figured, 

 of a " black glass interspersed with numerous residuary particles of 

 unfused silicates, which passes down gradually into the unaltered 

 granular stone. Sections of the thick blebby glass from the lower 

 surface show air vesicles and numerous crystallites imperfectly se- 

 creted from the glassy base, and too small to be seen in the figure, 

 together with the residuary unfused particles of the original min- 

 erals." 



Many of the stony meteorites are traversed by small, black, thread- 

 like veins, which are plainly due to a fracturing of the stone prior 

 to its entrance into our atmosphere. A greatly enlarged section of 

 one of these from the Bluff, Fayette County, Texas, meteorite is 

 shown in figure 2, Plate 7. The filling material of the vein is of 

 a nearly coal black color, opaque, and of an undetermined nature, 

 while the white and gray particles are fragments of the minerals 

 composing the body of the stone. Occasionally a slight movement 

 between the walls of these veins has developed a structure known 

 as slickensides in terrestrial rocks. In the illustration shown no 

 such movement has taken place, and it will be noted that the black 

 vein material penetrates into the walls in the form of small veinlets 

 on either hand. 



One other feature which may be mentioned is the occurrence of a 

 colorless, limpid, interstitial mineral, nearly or quite isotropic, which 

 forms one of the principal constituents of the meteorite of Shergotty, 



1 Zeits. d. D, geol. Ges., 1881, p. 25. 



