48 MAGIE— METEOR CRATER, ARIZONA. [April 22, 



at which the Widmanstatten figures disappear, the heat developed 

 in the siHca would then be equivalent to 2.3 X 10^^ ft. tons. 



The work done in the silica is surely only a fraction of the whole. 

 A layer of hard limestone, 300 ft. thick, was also broken up, and 

 much of it must have been pulverized also. After all, we can do no 

 better than guess; but taking all the work done into account we 

 may, in my opinion, estimate it without exaggeration, at 60 Xio^- ft. 

 tons. 



Such a projectile as would have made the crater would have 

 reached the earth without retardation by the atmosphere. If it were 

 moving, as a comet does, with the parabolic velocity of 25 miles a 

 second, and were to encounter the earth head on, it might fall with 

 a velocity something over 43 miles a second. We may set the 

 outside limits of velocity at 3 and 48 miles a second. With the 

 lowest velocity the mass required to bring in the estimated energy 

 is 15 X 10" tons; with the highest velocity only 60.000 tons. 



The mass of the meteor may otherwise be estimated from the 

 size and shape of the crater. Experiments with cannon shot, quoted 

 by Mr. Tilghman, show that with velocities of 1,800 ft. a second, the 

 depth of the hole made in limestone rock is about twice the 

 diameter of the shot, and its width at the top about five times the 

 diameter. These proportions were well borne out by observations 

 with spherical rifle balls shot into sandstone. If these proportions 

 held for the crater they would indicate a projectile 750 ft. in 

 diameter, with a mass of about 50 X 10^ tons. This is evidently an 

 over-estimate. The mass indicated in this way is however of the 

 same order of magnitude as the greatest mass indicated by the 

 estimates of the energy and velocity. Manifestly the extreme veloci- 

 ties estimated are not probable, so that the mass is probably neither 

 so large nor so small as the extreme values obtained. A mass of 

 400,000 tons moving with a velocity of from 18 to 20 miles a second 

 would bring in the estimated amount of energy. In the absence of 

 other evidence this seems a reasonable mass to assign to the buried 

 meteor. 



