I9I0.] METEOR CRATER, ARIZONA. 47 



rock masses all around the rim to a height of lOO ft. Perhaps 

 20 X 10^'^ foot tons spent in mechanical lifting would not be an 

 overestimate. 



Most of the energy was spent in breaking up the rock, and 

 especially in shattering the grains of sandstone into the very finely 

 pulverized silica. Only a rough guess can be made of the amount 

 of this silica, but large parts of the ejecta consist of little else, and 

 the borings have shown that the crater also contains great cjuantities 

 of it. From the probable size and shape of the whole cavity it 

 appears that over 500 million tons of rock were broken up. Of 

 these, perhaps one fifth, or 100 million tons, are in the form of 

 pulverized silica. The work done when this silica was formed was 

 expended in separating the particles and in rubbing them over each 

 other. The work done against friction must have been retained 

 as heat. The temperature generally did not rise to the melting tem- 

 perature of quartz, for the grains of silica rarely show evidence 

 of fusion. A small quantity of melted quartz is found, which is 

 full of blow holes, as if, when melted, the mass had been pervaded 

 with an expansible vapor. One way of explaining this formation 

 is to suppose that it represents the fusion of the shattered quartz 

 in the presence of water, which is known to be present occasionally 

 in pockets in the generally dry sandstone, the superheated steam 

 formed at the same time accounting for the porous state of the 

 material. If this explanation is correct, it indicates that the tem- 

 perature of much of the silica was nearly that at which quartz 

 melts when dry, and above the temperature at which it melts in 

 the presence of water. If we set, as an outside limit of temperature, 

 2500° C, and suppose all the silica heated to that extent, the 

 heat developed is equivalent to 9.25 X 10^^ ft. tons. It is possible 

 to ascribe the melting of the quartz to the heat more directly 

 developed in the neighborhood of the advancing meteor. In this 

 case it is more difficult to fix a lower limit of temperature for the 

 silica. The iron found outside the crater in the silica shows no 

 evidence of melting, and the Widmanstatten figures are preserved. 

 If we assume the general temperature of 625°, to keep it not only 

 below the melting point of iron, but also below that temperature 



