MERRILL] METEOR CRATER OE CANYON DIABLO, ARIZONA 485 



both have the same origin would seem most probable. Foote de- 

 scribed the material as "identical in appearance with an incrustation 

 which covered the surface of some of the irons or filled the pittings 

 in the same." Its occurrence in such large quantities he though in- 

 dicated that an extraordinarily large mass, of probably 500 or 600 

 pounds weight ( !), had become oxidized while passing through the 

 air, and so weakened that it burst into pieces not long before reaching 

 the earth. It is needless to state that Foote's estimate of the size 

 of the meteoric mass was at least conservative. 



Derby, writing in 1895, advocated the idea of the origin of the 

 schistose masses by secondary alteration — i. e., terrestrial weathering. 

 This view was generally accepted, but the question was opened 

 up again through the publication of Messrs. Barringer and Tilgh- 

 man, the first named, after noting the distribution of the material 

 as coextensive with the iron, stating his belief that it was produced 

 by the heat generated from friction while the meteor passed through 

 the earth's atmosphere. And again (p. 877) : "We have assumed 

 that these small particles (*. e., of shale in form of fragments and 

 spherules) once constituted a portion of the great luminous tail of 

 the meteoric body." 



Mr. Tilghman puts the matter a little more definitely in stating 

 that it "is fused and massive and at the same time stratified and 

 laminated and in general appearance different from any terrestrial 

 magnetite known, and closely resembles what would be thought, 

 a priori, to be the appearance of such a product of iron melted 

 and burned on the surface of a great meteorite in its passage through 

 the air." 



In explanation of the term "magnetite" as used by Mr. Tilghman, 

 it may be said that the particles are almost invariably somewhat 

 magnetic — more so, in fact, according to Mr. Barringer, than are 

 the irons themselves. This has led to the assumption that they are 

 composed, in part at least, of iron in the form of magnetite. Nichol's 

 analyses, as given by Farrington, 1 showed the material to consist 

 mainly of iron in the form of FeO and Fe 2 3 with smaller amounts 

 of the other constituents characteristic of the unaltered material. 

 From these analyses Farrington made the calculation of the con- 

 stitution of the shale as below : 



Limonite 52 . 99 



Magnetite 42 . 39 



Schreibersite . 64 



Graphite o. 15 



1 American Journal Science, vol. xxn, 1906, p. 303. 



