876 PROCEEDINGS OF THE ACADEMY OF [DeC, 



terial. Some of them contain holes or cavities which were probably 

 once occupied by nodules of troilite (sulphide of iron). Such nodules 

 are beautifully shown by sawing through some of the larger specimens 

 in the Ward and other collections. When exposed to the action of 

 the atmosphere these have oxidized, leaving the cavities they had 

 occupied. Occasionally some of the specimens have a noticeable 

 amount of iron oxide or shale adhering to them, but as a rule they are 

 very free from this. They are usually covered, however, with a very 

 thin film of iron oxide, which may be easily rubbed off with a wire 

 brush if the specimen has been previously heated. When this is done 

 their appearance would indicate that they may have been torn or 

 burned from presumably similar material. 



It is a fact worthy of note that so far none of these specimens of 

 meteoric iron have been found at any depth beneath the surface. 

 They are usually lying on the surface or partially or wholly covered by 

 the merely superficial soil, and are distributed, as already stated, more 

 or less concentrically around the crater, most of the small specimens 

 being found, however, to the north and northeast. That there are 

 great numbers of them contained in the thin soil overlying the solid 

 limestone composing the level plain on all sides of the mountain is 

 proven by the fact that we have found several specimens, from seven 

 pounds to twenty-seven pounds in weight, so imbedded in digging a 

 trench for a pipe line from Canon Diablo gorge to the crater. They 

 have not been found in the numerous cuts or shafts which have been 

 made in the silica. Four of them, weighing three or four pounds each, 

 have been found on the interior of the crater, and, so far as I know, these 

 are the only iron specimens which have been found inside of the crater. 

 These were found above the cliffs already described. Considerable 

 "iron shale" has also been found inside the crater, among the talus at 

 the base of the cliffs. I shall propose hereafter a possible explanation 

 of the fact why these irons are found only on the surface. It is also 

 worthy of note, as already stated, that we have found more of the smaller 

 irons, on or in the surface soil, on the north and northeastern portion 

 of the rim than in other places. 



Now there have been found abundantly distributed around the 

 rim, and especially on and in its northern portion, and nearby on the 

 plain, very large quantities, probably aggregating a ton or more in 

 weight, of magnetic oxide of iron. This is so abundantly distributed 

 over the northern surface of the rim and over the surrounding plain, 

 and is so apparent to the casual observer, that it seems wonderful 

 to me that Mr. Gilbert and his associates did not make any reference 



