THE STRUCTURE OF METEORITES 55 



processes of corrosion and decomposition go on if the meteorite 

 is exposed on the earth's surface for any length of time, which 

 may have their effect on the structure of the meteorite. These 

 therefore must be judged and eliminated. Again, the fissures 

 found in meteorites are believed by many to be the result of 

 cracking from the sudden development of heat caused by the 

 entry of the mass into the earth's atmosphere and the veins 

 of meteorites are by some thought to be fissures filled by matter 

 fused by such heating. Due weight must be given these pos- 

 sible effects and all that are certainly of terrestrial origin 

 must be left out of consideration. 



Uniformity of mass structure of single meteorites. — The iron 

 meteorites usually show remarkable uniformity of structure 

 throughout. Sections from different portions of a single mass 

 or even different masses of the same fall usually give on 

 etching, figures so similar that the meteorite to which they 

 belonged can be recognized at a glance, even if the specimens 

 have been widely separated. In some, however, there are varia- 

 tions in the same mass. Thus the Floyd county iron according 

 to Kunz and Weinschenk while possessing a generally cubic 

 structure shows portions which are granular ; the Linnville iron 

 according to Kunz is partly of cubic structure and partly amor- 

 phous. The Carlton iron is partly rich in plessite and partly 

 poor in plessite. The Holland Store iron has portions coarse- 

 grained and fine grained. Four of the five masses found near 

 Staunton, Virginia, are quite similar in structure, showing on 

 etching, figures made up of short, swollen bands. The etching 

 figures of the fifth mass are, however, made up of long, straight 

 bands. Moreover the taenite of the first four is brittle, of the 

 fifth elastic. So sharply does the latter mass differ from the 

 others that Brezina regards it as belonging to a different fall, 

 but it is more likely that the differences are those of structure. 

 Such exceptions are however so rare as to emphasize the fact 

 that on the whole iron meteorites are uniform in structure. 

 Speaking in a general way the iron-stone and stone meteorites 

 are likewise uniform in mass characters although such as are 



