iio Field Columbian Museum — Geology, Vol. III. 



is that two ataxites fell at different times at one locality. In view 

 of the small number of ataxites. known, this seems less likely than 

 to suppose that two masses of the same fall differed in composition. 

 No other case of such marked difference is known. Differences of 

 structure seem as a rule to be a better criterion for distinguishing mete- 

 orites than differences of composition. On the other hand, similarity 

 of structure and composition together do not positively identify 

 meteorites found at different places as belonging to one fall, since 

 such similarities occur in meteorites seen to fall at widely different 

 times and places. Of the nine iron meteorites seen to fall, four are 

 medium octahedrites and have practically similar compositions. In 

 correlating individual meteorites, therefore, all possible characters 

 must be taken into consideration, including the circumstances of 

 their find, the appearance of their exterior, the probable time elapsed 

 since their fall, etc. 



No attempt has been made by the writer at summation of the 

 analyses here given, in order to determine the average composition of 

 iron meteorites. Such a summation, if worthy of being performed at 

 all, will be deferred until analyses of the iron-stone and stone meteor- 

 ites are also at hand for comparison. This work the writer hopes to 

 accomplish in the near future. It is obvious, however, from an inspec- 

 tion of the tables that the average percentage of iron in iron meteor- 

 ites as a whole is not far from 91 per cent, while that of nickel closely 

 approximates 7.50 per cent. It is doubtful if the average percentage 

 of the remaining minor constituents can be learned by summation of 

 existing analyses. Not only have these constituents in many cases 

 not been determined, but also any slight error in analyses or sampling- 

 would double or multiple their percentage. A percentage of .4 of 

 cobalt, for instance, as compared with .2, is within the limits of error 

 of many analyses, yet one percentage is double that of the other. The 

 same is true in much greater degree of determinations of the amount 

 of copper and other constituents. Until a larger number of complete 

 and accurate determinations are at hand, therefore, summations of 

 these constituents seem to have little value. One point in the compo- 

 sition of iron meteorites which may or may not be of significance may 

 be noted. Of the four constant metallic constituents, the most 

 abundant, iron, has the lowest atomic weight, the next in quantity, 

 nickel, is next higher, and so on for cobalt and copper. This grada- 

 tion, using percentages common in iron meteorites, appears as follows: 



Iron. Nickel. Cobalt. Copper. 



Per cent in iron meteorites 90 9 0.9 0.02 



Atomic weight 55.5 58.3 58.6 63.1 



