912 PROCEEDINGS OF THE ACADEMY OF [DeC, 



ited yesterday. This will give a superior limit of time within which 

 the fall must have occurred from whatever rate may be assigned to the 

 erosion of the red sandstone buttes. The author would name 10,000 

 years as the utmost possible limit which could be allowed, and feels 

 that this is much too liberal and that something well inside of 5,000 

 years is much more nearly in accordance with the facts. In fact, so 

 recent is the appearance of everything in this locality that some stunted 

 cedars, growing on the rim and showing year rings of over 700 years of 

 growth, are not without value in placing a minimum limit within which 

 the fall cannot have occurred. 



Size of the Meteorite Forming the Hole. 



Of this it is extremely difficult to form any idea from data which 

 would stand critical exainination. Professor Gilbert put the necessary 

 minimum as the equivalent of a sphere of 750 feet in diameter, and 

 the probable size as equivalent to a sphere of 1,500 feet in diameter. 

 This seems to the author as most excessive. The problem contains 

 too many unknown factors to make calculation much, if any, better 

 than guesswork. The following facts may be considered as having 

 some bearing in assigning a possible maximum size to the projectile. 

 The artillery tables above referred to give a penetration of something 

 less than two diameters in solid limestone rock for shot at about 1,800 

 feet per second. Xow, from the prol^able absence of meteoric material 

 in the hole below 500 feet, this is assumed as about its limit of penetra- 

 tion. This corresponds to a penetration of about 900 feet of solid rock 

 on the whole considerably softer than limestone, and would therefore 

 correspond to a sphere of considerably less than 450 feet in diameter, 

 if the velocity were not in excess of 1,800 feet per second. Xow what 

 this striking velocity was can only be guessed at, although it is abso- 

 lutely certain that it was in excess of 1,800 feet per second, in all proba- 

 bility many times in excess of this figure; and it must be kept in mind 

 that the energy would increase as the square of the velocity, and that 

 the cubic contents of the hole excavated would vary directly with the 

 energy exerted. Therefore if the velocity was 9,000 feet per second, or 

 five times that quoted above, a sphere of one-twenty-fifth the weight of 

 the above would deliver the same amount of energy and therefore prob- 

 ably make the same sized hole. The original velocity of any such body 

 is reasonably well known from astronomical considerations and it prob- 

 ably struck the atmosphere at between nine and forty-five miles per 

 second, depending upon the direction of its motion in relation to the 

 motion of the earth. We know that this excessive velocitv is verv soon 



