44 BULLETIN 149, UNITED STATES NATIONAL MUSEUM 



tallization of the finely granular interstitial silicates in stones of the 

 eukrite and howardite groups. 



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

 Uke veins, at most but a few millimeters in diameter (fig. 2, pi. 29) 

 which are plainly due to a fracturing of the stone, though whether or 

 not prior to entrance into the earth's atmosphere is a question. A 

 greatly enlarged section of one of these from the Bluff, Fayette County, 

 Tex., meteorite is shown in Figure 2, Plate 28. The filling material 

 of the vein is of a nearly coal black color, opaque, and of an undeter- 

 mined nature, inclosing white and gray particles 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 coloring 

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

 either hand. Much discussion has taken place concerning the origin 

 of these veins and a great divergence of opinion manifested, a part 

 of which is evidently due to mistaken ideas regarding the nature of 

 the filling material, often referred to as "metallic." As a matter of 

 fact, the material is metal in comparatively few cases, but is apparently 

 identical both in composition and origin with that forming the base 

 of the so-called black chondrites, and can best be accounted for through 

 a slight modification of the idea expressed by Wahl, the shock from a 

 collision producing the fracture, along which is immediately prop- 

 agated a heat wave sufficient to produce the result. In this way the 

 minute ramifications (spirts) of the vein matter into either wall, as 

 shown in the figure, would be readily accounted for. The occasional 

 presence of metal, or metallic sulphide, as an apparent filling con- 

 stituent, can be best explained as has Farrington ^^ on the assumption 

 that either constituent occurred in the form of more or less connected 

 filaments. Fracturing would naturally take place along these lines 

 rather than across them. That heat could have melted the metal 

 without affecting the silicates is impossible, and that the filling matter 

 is not of the same nature as the crust (that is, a glass) is almost 

 self-evident. 



That collisions among meteorites are not limited to the stony forms 

 is strikingly shown in Figure 1, Plate 29, from a polished slice of an 

 iron meteorite found a few years ago in Somerset County, Pa. It 

 will be noted that the iron is traversed by a fine, thread-like fissure 

 along which has taken place a movement for a distance of something 

 like a centimeter. In short, it is like a fault in terrestrial rocks. As 

 the iron is soft and malleable, we are apparently justified in the 



89 Amer. Journ. Sci., vol. 11, 1901, p. 59. 



