1914.] NATURAL SCIENCES OF PHILADELPHIA. 503- 



barded and the earth so seldom bombarded during recent geological 

 history is seemingly difficult to explain, but one must not forget that 

 the moon has been without an atmosphere for perhaps a great many 

 million years and all the bombardment to which it has been subjected 

 during this vast period of time is clearly and permanently recorded. 



May it not be possible that when one holds in his hands one of 

 the meteorites that occasionally reach this earth and which reached 

 it on its present surface in far greater numbers at and around Meteor 

 Crater in Arizona than any other locality known to us, he is holding 

 in his hands something older than our sun or any of the planets which 

 revolve about it; in fact, that he is holding in his hands something 

 which has literally formed part of the nebula out of which our whole 

 solar system has been built up? If this be in accordance with the 

 facts it would help to confirm the more recent theories of the building 

 up of the planetary systems as put forward by Chamberlin and 

 jMoulton. 



It seems to me to be not inappropriate to bring this paper to a 

 close by quoting in substance an argument which I recently heard 

 used by Dean W. F. Magie, Professor of Physics at Princeton Uni- 

 versity, in favor of the impact theory of origin of the Arizona crater 

 and as against the steam explosion theory of origin, which has l^een 

 advanced and persisted in notwithstanding all the evidence pre- 

 sented in the many papers which have been written on the subject 

 since the publication of my first paper read before The Academy of 

 Natural Sciences of Philadelphia. Dean Magie spent a fortnight 

 at Meteor Crater several years ago studying the various phenomena 

 in connection with the crater and carefully checking the statements 

 of fact made by me in the National Academy paper above referred 

 to. The argument is as follows: 



First, on the doctrine of probabilities, the chances are one in 

 many millions that the greatest known shower of iron meteorites 

 should have fallen on the exact spot, with the Arizona crater as the 

 centre of its distribution (by consulting Plate XXIII it will be noticed 

 that the meteorites increase in number as one approaches the crater) , 

 at which a single, unprecedented steam explosion on a rapidly 

 revolving earth occurred. 



• Secondly, that the chances are one in many more millions that 

 this shower should have fallen on the exact site chosen for such an: 

 unprecedented steam explosion at the same instant of time that the 

 steam explosion occurred. 



Thirdly, that the chances are again one in millions that the steam 



