Januaky 3, 1896.] 



SCIENCE. 



acter to the known, and this suggestion con- 

 stitutes the pi-oduction of a hypothesis. 



To test this hypothesis of liypotheses I 

 have for some years endeavored to analj'ze 

 the methods employed by myself and some 

 of my associates in geologic research, and 

 this study has proved so interesting in 

 connection with the investigation of a pe- 

 culiar crater in Arizona, that I shall devote 

 the remainder of my hour to an outline of 

 that investigation. 



Fig. 1. — Map of part of northern Arizona. The 

 shaded areas are covered by volcanic rocks. Dots 

 mark ancient volcanic vents. 



In northeastern Arizona there is an arid 

 plain beneath whose scanty soil are level 

 beds of limestone. At one point the plain 

 is interrupted by a bowl-shaped or saucer- 

 shaped hollow, a few thousand feet broad 

 and a few hundred feet deep ; and about 

 this hollow is an approximately circular rim 

 rising one or two hundred feet above the 

 surface of the plain (Plate 1, Figs. 2 and 

 3). In other words, there is a crater ; 

 but the crater differs from the ordinary vol- 

 canic structure of that name in that it con- 

 tains no volcanic rock. The circling sides 

 of the bowl show limestone and sandstone, 

 and the rim is wholly composed of these 

 materials. On the slopes of this crater and 

 on the plain round about many pieces of 

 iron have been found, not iron ore, but the 

 metal itself, and this substance is foreign to 



the limestone of the plain and to all other 

 formations of the region.* The features of 

 the locality thus include three things of un- 

 usual character and requiring explanation : 

 First, the crater composed of non-volcanic 

 rock ; second, the scattered iron masses ; 

 third, the association of crater and iron. 

 To account for these phenomena a number 

 of theories have been suggested . 



In the year 1886 a company of shepherds 

 encamped on the slopes of the crater aud 

 pastured their sheep on the surroiinding 

 plain. Mathias Armijo, one of their num- 

 ber, found a piece of iron, and, deceived by 

 its lustrous surface, supposed it to be silver. 

 The mistake was quickly corrected by his 

 fellows, but his discovery excited . their in- 

 terest, and other pieces of iron were soon 

 found. The curiosity of the shepherds 

 was aroused also by the crater, and they 

 invented a theory which is admirable for 

 its simplicity: The crater was produced 

 by an explosion, the material of the rim 

 being thrown out from the central cavity, 

 and the iron was thrown out from the same 

 cavity at the same time. You will observe 

 that this theory is comprehensive. It ac- 

 counts for the crater, the iron, and the as- 

 sociation of tiie two. As I have never met 

 these first students of the phenomena I 

 have had no opportunity to make inquiry 

 as to the origin of their theory ; but its 

 close relation to the theories of geologic dis- 

 turbance which are current in mining dis- 

 tricts suggests that it also sprung from the 

 familiar process of blasting. As the firing 

 of a blast opens a cavitj'^ and heaps dislo- 

 cated rock masses in an irregular way, the 

 unlearned miner finds in natui'al blasting 

 an easy explanation of hollows and uplifts. 



Four years later a man by the name of 

 Craft saw in the iron a possibility of profit. 

 Setting up a heap of stone to mark the spot, 



* Tlie crater is locally known as Coon Mountain, or 

 Coon Butte. The iron is known to literature as the 

 Canyon Diablo fall of meteorites. 



