234 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1932 



up to 5^ cm in thickness indicates that the iron has suffered con- 

 siderable oxidation by weathering. Many of the smaller pieces of 

 iron are flaky and shell-like with convex and concave surfaces, and 

 they often show fantastically twisted forms. In one or two cases 

 such a shell-like flake is only loosely attached to a larger piece. It 

 therefore seems probable that many of the smaller pieces are the 

 result of the breaking down of larger masses by oxidation. 



From my examination of the 60-ton Hoba meteorite, buried in situ 

 with its enveloping zone of " iron shale," I am convinced that the 

 concave and pitted surfaces so commonly shown by iron meteorites 

 are the result of subsequent weathering rather than of burning dur- 

 ing the brief flight through the atmosphere. This pitting is no doubt 

 due to the decomposition of the particles of troilite (FeS) scattered 

 through the iron. The surface of the Henbury irons, with a skin of 

 glazed limonite, is quite different from that of the few iron meteorites 

 which have been actually observed to fall. 



The presence of the " iron shale " supports Mr. Alderman's conclu- 

 sion that the fall of the meteorite took place ages ago. Mr. R. 

 Bedford is, however, of the opinion that the fall is comparatively 

 recent. On his return journey he interviewed, at Oodnadatta, Mr. 

 J. M. Mitchell, a local prospector, who had known of the masses of 

 iron 12 years ago. Mr. Mitchell asserted that the old blacks would 

 not camp within a couple of miles of the place, and that they called 

 it " chindu chinna warn chingi 3'abu," meaning " sun walk fire devil 

 rock." 



An etched section of the iron shows well-marked Widmanstiitten 

 figures of the medium octahedrite type. Besides kamacite, taenite, 

 and plessite, there are a few minute specks of troilite. The kamacite 

 bands, instead of being straight, are wavy and in places much curved 

 and distorted. During the process of etching no straight and definite 

 Neumann lines were detected, but the kamacite bands are marked by 

 wavy lines and an irregular network of cracks. This would indicate 

 a disruption of the mass, wliich may have taken place at the time of 

 fall or at some earlier period. 



Mr. Alderman's paper is a valuable contribution to the scanty 

 knowledge of the problematical meteorite craters ; and in the case he 

 describes the association of meteorites with the craters could scarcely 

 be fortuitous. Meteorite fragments have been also found around the 

 single craters of Canyon Diablo (Arizona) and Odessa (Texas), but 

 none near the craters of Tunguska (Siberia) and Kaali (Esthonia)." 

 Around the 60-ton Hoba (Southwest Africa), the largest known 

 meteorite, there is no sign of a crater. 



8 Mill. Abstr., vol. 4, pp. 427-428, 19.31 ; vol. 5, pp. lG-17, 1032. 



