2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I07 



Though in places the bands are closely grouped, plessite fields are 

 relatively large and very abundant, and are mostly of the "dense" type 

 consisting of imperfectly transformed gamma-alpha aggregate. 



A few plessite fields show spheroidized taenite in a ground mass 

 of clear kamacite, a feature that is being observed with increasing 

 frequency as more meteoric irons are studied by metallographic 

 methods. This structure appears to be due to a condition of cooling in 

 which the taenite in the original gamma-alpha mixture was fully 

 transformed but, because of too rapid cooling, could not migrate to 

 the boundaries of the field to form the usual taenite border. 



Near the edge of one of the slices there are traces of a zone of 

 heat alteration, containing round bodies of an Fe-FcsP eutectic. 

 These bodies, which have been observed in a number of other irons, 

 are apparently due to the melting of schreibersite inclusions within 

 the zone of alteration. Such fused inclusions, having absorbed iron 

 (kamacite) from the surrounding mass, rejected the excess of the 

 iron above the eutectic ratio in cooling, the excess separating as 

 droplets or (as in this case) in the form of dendrites. 



Composition of Edmonton iron. — A thin slice was cut and etched in 

 order to develop the structures and make more conspicuous any in- 

 clusions or structural irregularities. A portion was selected which 

 represented as nearly as possible the average pattern of the meteorite. 

 Care was taken to exclude any visible inclusions from the sample 

 used for the analysis. Meteorites are not homogeneous, and samples 

 selected for analysis should not contain avoidable inclusions. 



The chemical analysis reported represents a sample with average 

 widmanstatten structures for this iron, and although the meteorite 

 carries inclusions of troilite and schreibersite, no phosphides or 

 sulfides apparently exist as disseminated small particles in the com- 

 ponents which make up the average structure. 



The following table shows analyses of the Edmonton, Ky., and the 

 Carlton, Tex., irons. These two individuals have a very similar 

 structural pattern and are also nearly identical in composition. 



The specific gravity of the Edmonton iron was determined upon 

 two different portions, both assumed to be free from inclusions. The 

 gravity is only slightly lower than that reported by Eakins for the 

 Carlton iron. 



The radium determinations were made by Gordon L. Davis and 

 William D. Urry, of the Geophysical Laboratory in Washington, D. C. 



The molecular ratios for iron, nickel, and cobalt are obtained by 

 dividing the percentage of each element found by the atomic weight 

 of the element. The significance of these nickel, cobalt to iron, molec- 



