308 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 3 



the smaller pieces of meteoric iron from Wabar when sectioned, pol- 

 ished, and etched show a partial destruction of the characteristic 

 structure such as can be brought about artificially by heating the 

 material to about 850° C. 



Now the close association of silica glass and meteoric iron with a 

 group of craters in a sandy desert can be accounted for in no other 

 way but by the impact of a shower of large meteoric masses. We 

 have, in fact, at Wabar a typical example of meteorite craters. 



It is my present purpose to give some account of the few meteorite 

 craters or supposed meteorite craters that have so far been discov- 

 ered, in the hope that the scanty information at present available 

 may be of some help to travelers in recognizing further examples. 

 There are many craterlike depressions on the earth's surface, but it 

 would be rash to assume that all have been formed by the fall of 

 meteorites. Some other pieces of evidence must be sought for. Noth- 

 ing is yet known of the mechanics of the formation of such craters. 

 They are not merely dents or holes made just by the projectile force 

 of the meteorite as hitherto supposed. They appear, rather, to be 

 explosion craters due to the sudden vaporization of part of the 

 material, both of the meteorite and of the earth, in the intense heat 

 developed by the impact. 



The meteorite craters so far described may be easily remembered 

 by the following classification, with two examples in each class : 



Single craters with associated meteoritic material (Arizona and 

 Texas). 



Groups of craters with associated meteoritic material (Central 

 Australia and Arabia). 



Groups of craters without associated meteoritic material (Estonia 

 and Siberia). 



Single craters without associated meteoritic material (Ashanti and 

 Persia). 



This makes a total of eight examples. It seems a pity to disturb 

 this beautifully symmetrical arrangement, but farther on I shall add 

 a third example to the second class, while the third and fourth classes 

 are not proved, and the last example is more than doubtful. That 

 leaves only five more or less certain examples of known meteorite 

 craters. 



The Arizona crater (pi. 1) was first brought to notice in 1891 by 

 the discovery of many masses of meteoric iron scattered around the 

 crater.* The finding of diamond in this iron aroused a considerable 

 amount of interest and not much notice was at first taken of the 



* Foote, A. E., A new locality for meteoric Iron with a preliminary notice of the 

 discovery of diamonds in the iron. Amer. Journ. Sci., ser. 3, vol. 42, pp. 413-417, 2 pis., 

 1891; and Proc. Amer. Assoc. Adv. Sci., vol. 40 (for 1891), pp. 279-283, 1892. 



Accounts of the crater have been given by : 



