NICKEL-IRON OXIDES 499 



To summarize : all the phenomena thus far found in the long and care- 

 ful exploration of the crater, the distribution of the wreckage both inside 

 and outside, and the composition and structure of the materials seem to 

 be fully and satisfactorily explained on the theory of impact by a celestial 

 bolide of high velocity, and do not fit any other theory. 



The Nickel-ihon Oxides 



The association of the Canyon Diablo siderites with the crater needs 

 no discussion here, but it may be said that the distribution of the irons 

 over the crater rim and the surrounding plain has been found much more 

 general and extended than was formerly known; but an important new 

 fact is the general occurrence along with the irons, and also in the wreck- 

 age, of iron oxides of meteoric origin. The existence of these oxide 

 masses is not a new discovery, having been noted by Doctor Foote, but 

 their meteoric nature, their abundance and wide dissemination, and their 

 intimate relationship to the phenomena have not been appreciated. Pos- 

 sibly the oxide fragments were confused with the abundant nodules of 

 ordinary limonite derived from the country rocks and scattered over the 

 plain and crater rim. 



Many oxide masses, up to large size, have a globular form with more or 

 less concentric structure and lamination, apparently due to weathering 

 and hydration from an original metallic mass. A siderite core is fre- 

 quently found which appears on cut and etched section much like the 

 Canyon Diablo irons, though the crystalline structure seems somewhat 

 different. Such masses with metallic cores have been found in the silica 

 of the outer slopes to the depth of 27 feet, while multitudes of frag- 

 ments, evidently derived from disrupted nodules, are -found over and in 



blow, and this powder, being stiU further compressed, transmits tlie pressure upon it in 

 all directions, somewliat like a fluid, although not equally in all directions. The 

 pressure thus generated in the very substance of the material seeks relief and forces a 

 yielding of the solid material around it, which, of course, occurs along the line of least 

 resistance, and bursts the surface upward and outward into a cone-shaped crater around 

 the point of impact or pressure, the angle of which depends largely upon the nature of 

 the material. 



"The bearing of this upon the formation of a rim composed in part of fine powder is 

 as follows : The broken rocks and debris that are expelled from the hole get their velocity 

 Imparted to them by the push of an inelastic powder, and not by a compressed elastic 

 gas, and thus, when both rock fragments and powder have progressed far enough to free 

 themselves from the pressure of the penetrating projectile, they fly on together, mixed 

 powder and rocks, at the same velocity. This powder is not dust in the ordinary accep- 

 tation of the word, as flue powder mixed with a large quantity of air, which takes a 

 long time to settle out, but is almost unmixed with air in solid masses, particle to par- 

 ticle, like flour in a barrel, so to speak ; which masses obey the laws of projectiles and 

 falling bodies, irrespective of the exceedingly minute particles of which they are formed, 

 and are thus deposited in the rim in mixture with and under and over the solid rock 

 masses which accompanied it in its flight, and as quickly." 



