24 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



meteorite to fall unnoticed in Chile, How these two localities would 

 compare if both were as effectively prospected is problematic. 



The arid climate of northern Chile favors preservation of mete- 

 orites. Stony meteorites from there should be less contaminated than 

 those recovered from more humid areas because, without water, 

 contamination is less likely to penetrate a meteorite. However, 

 exposed meteorites in arid places can suffer from another type of 

 weathering — wind ablation, which, in time, could be an effective way 

 of obliterating a meteorite. Some irons from arid regions have 

 sculptured surfaces that demonstrate how one constituent is ablated 

 faster than another. Wind ablation is relatively rapid compared with 

 chemical weathering in arid areas. The products of mechanical 

 ablation might be confused with meteoritic dust, because undoubtedly 

 some of the metallic iron is removed and accumulates in the wind- 

 blown silt. 



Many years ago the author called to C. A. Bauer's attention the 

 possible identity of the northern Chilean hexahedrites and later 

 furnished him with specimens for study. These specimens apparently 

 were later turned over to Signer and Nier (1962), whose measure- 

 ments are presented in tables 9 and 10, although in a somewhat 

 different order so as to arrange the meteorites in their order of 

 increasing latitude. 



Signer and Nier (1962), in discussing the possibility of these 

 Chilean irons being a common fall, said : 



Due to the low concentration of cosmogenic rare gases in these samples, the rela- 

 tive errors in these measurements may be somewhat higher than the 5% found 

 for most other measurements ; unfortunately, the samples available were so small 

 that only a single analysis was possible and therefore, no check of reproducibility 

 could be made. With this reservation, it seems possible that the Tocopilla, Coya 

 Norte and Rio Loa belong to the same fall. Negrillos, however, appears to 

 belong to a different fall. It should be mentioned that by nature of the inter- 

 pretation two meteorites could by coincidence appear to belong to the same fall. 

 The converse does not appear possible. 



The overall scatter of the Chilean hexahedrites extends from about 

 20° to 24° S. latitude, while the three irons that Signer and Nier 

 suspected of being related He between 21°26' and 22°40' S. latitude. 

 Thus, the Rio Loa, Coya Norte, and Tocopilla are confined within 

 about 70 miles of the overall spread of about 240 miles for these 

 Chilean hexahedrites. 



