1905.] NATURAL SCIENCES OF PHILADELPHIA. 899 



proportion to their iron than fovuid in the irons themselves and in the 

 larger pieces of magnetite. This is not a usual substance and, so far 

 as known, is not a constituent of any of the rocks in the neighborhood 

 of the area anywhere adjacent to the same. 



Ox THE Fine Silica Powder under the Base of the Rim. 



The meteoric theory of the formation of this hole being thought 

 untenable by some previous investigators and the ordinary volcanic 

 action being absent, there has been invoked, to account for its formation, 

 the theory of a single steam explosion, and in fact this theory has been 

 elaborated so far as to try to imagine a state of stress produced by steam 

 which was set off by the blow of a small falling meteorite, much in the 

 same manner that a percussion cap discharges a gun. This was evolved 

 to account for the simultaneous deposition of the meteoric material 

 and the rim. This has been urged in spite of the fact that during the 

 time that the local heat had been increasing in the wet strata there 

 would have inevitably been hot spring action, and that the same thing 

 would have occurred long after the relief of the explosion, and that the 

 traces of this action would have been but little, if any, less evident than 

 those of ordinary volcanic action and are nevertheless totally absent. 

 Yet there is one fact obvious to all observers to-day, to which the 

 author desires to call attention, which makes any such theory of the 

 explosive formation of the hole utterly impossible. This is the fact 

 that the rim is generally founded upon a more or less deep layer of 

 fine silica powder. There is no doubt that the rock fragments forming 

 the rim were all deposited within a few seconds after the hole was made. 

 The great majority were propelled too short a horizontal distance to 

 have had a long trajectory in the air. Now if they had been propelled 

 by a compressed elastic medium, it is evident that on the explosion 

 these compressed gases would have instantly assumed a much higher 

 velocity than the heavy rock particles to which they were imparting 

 velocity and, sweeping by them, would have carried with them every 

 particle of silica powder which had been made by the crushing an^ 

 yielding of the strata to the strain, and the rocks of the rim would cer- 

 tainly and necessarily have fallen on the bare upturned stratum which 

 had previously formed the surface of the ground around the edge of 

 the hole. To account for the presence of this silica powder on the 

 theory that the hole was formed by a great projectile requires a short 

 preliminary study as to the yielding of hard, brittle and practically 

 incompressible material before a projectile or other blow or even quiet 

 pressure, for the method is much the same in both cases. Briefly, the 



