208 SMITHSONIAN MISCELLANEOUS COLLECTIONS [VOL. 50 



An attempt has been made by at least one writer to account for 

 these forms, some of which are of not over a gram in weight, on the 

 supposition that they were flaked off from the cold parent mass 

 through the superficial heat suddenly developed after the meteorite 

 entered our atmosphere. It is, perhaps, not safe, without experi- 

 mental work, to say how a mass of iron might behave under these 

 conditions. It should be borne in mind, however, that the Canyon 

 Diablo iron is one of the hardest and toughest of known meteorites, 

 and that, moreover, as has been apparently definitely shown, the depth 

 of the penetration of heat in such cases is extremely slight, owing 

 to the rapid stripping off of the burned or fused material during 

 its passage through the air. The discovery of this readily oxidizable 

 variety of what is apparently a part of the same fall 1 may, perhaps, 

 enable us to account for this phenomenon otherwise. 



The possibility of the irons being but residuals out of a large and 

 coarse-grained stony meteorite or pallasite has often been considered 

 by the writer and is discussed by Mr. Barringer. He fails to find 

 any evidence in favor of such a supposition. With these conclusions 

 the writer agrees. In comparing the large number of irons which 

 the Messrs. Barringer and Tilghman have placed in our hands we 

 think, however, we have been able to trace a tendency toward grada- 

 tion of one form into another. In cutting several which seemed nearly 

 identical with the well-known types, we found here and there appar- 

 ent intermediate structures (see upper right of pi. xx), and portions 

 rich in iron phosphide, with thin particles of shale adhering. We have 

 therefore come to the conception of a large heterogeneous mass of 

 nickel-iron with segregation masses rich in chlorides, phosphides, 

 and sulphides. Such would naturally rupture most readily along the 

 line of contact with the more homogeneous portions, and, moreover, 

 the results of atmospheric frictional heat would ignite and burn 

 away the sulphide portions. Even where the heterogeneous masses 

 of considerable size fall to the earth it is possible that these sus- 

 ceptible portions would oxidize and wholly disappear, leaving the 

 more refractory to be found later. This would account for the 

 almost constant association of shale .and irons of the type shown in 

 pi. xxi at various points out on the plain. 



The occurrence of the still incompletely oxidized forms — shale 

 balls — as described, is due to the protective action of the dry soil in 

 a region of great aridity, the annual precipitation, as recorded by the 

 Weather Bureau, being but about 8 inches. It has been shown by 

 the Bureau of Soils that under such conditions soils rarely or never 

 become saturated with moisture for more than a few inches below 



1 The possibility of an independent fall has been considered. 



