HENBURY METEORITE CRATERS ALDERMAN 229 



Crater No. 5 was considered to be the most suitable for this pur- 

 pose. A hole to the depth of 8 feet was sunk through fine loamy 

 soil. At this depth rock fragments, apparently washed inwards 

 from the walls, prevented further sinking. This showed that the 

 small crater No. 5 had originally been at least 8 feet deeper than it 

 now is. If any meteoric mass has penetrated to a depth of more 

 than 8 feet below the present floor of a small crater like No. 5, the 

 depth to which such a mass has penetrated below the larger craters 

 must be very considerable. 



An experiment was also made to see if a compass needle showed 

 any deviation on approaching and passing the Main Crater. Trav- 

 erses were made with this end in view, but the prismatic compass 

 used gave results which could not be considered beyond the limits 

 of experimental error. 



Although these observations gave results which can only be con- 

 sidered as negative, the author believes that further work along 

 these lines should be proceeded with as soon as possible. In such a 

 case as this the use of geophj^sical methods seems to be ideally suited. 

 If, as at the great Meteor Crater at Canyon Diablo in Arizona, mag- 

 netic methods prove to be somewhat unsatisfactory, it is highly 

 probable that good results would be obtained by the use of gravi- 

 metric, seismic, or electrical methods. 



EFFECTS OF IMPACT 



The excavating effect of the fall of a large meteoric mass is of 

 course self-evident, and the intense shattering and crushing of the 

 surrounding country rock are only to be expected. The walls in all 

 cases consist of unconsolidated fragmentary rock material varying in 

 size from the finest powder up to large masses several cubic feet in 

 volume. The effects of shearing stresses are also to be noted in 

 many specimens. 



Besides the formation of the 12 or more craters mentioned, the 

 impact of the meteoric bodies with the earth has left traces of other 

 effects which are extremely interesting. One of these phenomena 

 is shown particularly well by crater No. 3. Radiating outwards into 

 the plain from the crater walls can be seen five or six low ridges of 

 sandstone. These suggest " dikes " of a hard rock which has resisted 

 erosion more successfully than the surrounding country rock. They 

 consist, however, of sandstone which is apparently identical with 

 that to be found anj^where in the neighborhood. The " ridges " are 

 only a few inches higher than the surrounding surface of the plain, 

 but consisting as they do of small blocks of sandstone, of which the 

 surface is blackened due to weathering, they are easily distinguished 



