314 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1933 



The Wabar Craters, discovered by Mr. Philby ^^ in February 1932, 

 are in the Rub' al Khali at 21°29y2' N., 50°40' E. (pis. 3 and 4). 

 Two distinct craters were mapped with indications of two others 

 buried in the sand. Isolated patches of the slaggy material suggest 

 that still more craters are buried. The larger crater is approxi- 

 mately circular in outline with a diameter of 100 meters and a depth 

 of 40 feet (lOi^ meters). It shows a long gap in the rim on the 

 northern side. The smaller crater, 200 meters distant from the first, 

 is oval in outline with dimensions of 55 by 40 meters. The outer 

 slopes are gentle and the inner slopes steeper, and the bottom is filled 

 with drifted sand. For a distance of about 40 meters from the rim 

 the outer slopes are thickly strewn with cindery masses of silica 

 glass and smaller complete bombs of the same material, ranging in 

 size down to small " black pearls ", which were picked up in large 

 numbers. 



The rims of the craters appear to be built up mainly of this silica 

 glass. There are no rock fragments except as small angular pieces 

 o,f a sintered sandstone enclosed in the larger masses of silica glass. 

 Near the craters there is a small outcrop of a friable cream-colored 

 sandstone composed of small shattered grains of quartz, and this 

 presumably extends beneath the desert sand and the craters. 



On the outer slopes of the craters there were also collected a few 

 small pieces of meteoric iron and fragments of iron rust. A much 

 rusted mass of meteoric iron weighing 25 pounds was found about 

 200 meters northwest of the smaller crater and nearer one of the 

 buried craters. This must be only a weathered remnant of a much 

 larger mass, as it shows the normal octahedral structure unaffected 

 by heat. In the smaller pieces the kamacite is granulated. The 

 group of craters indicate that here there must have been a shower of 

 large masses of iron. 



The reason for the unique development of silica glass at Wabar 

 is no doubt that the large masses of iron fell on clean desert sand. 

 A remarkable feature of the bombs and black pearls is their extreme 

 lightness. Inside they consist of a very cellular white silica glass, 

 and they are coated with a thin skin of black glass, usually with a 

 highly glazed surface and often beset with minute pimples. The 

 black glass is brown and transparent, with only a few minute bub- 

 bles, when examined in thin sections under the microscope. Chem- 

 ical analysis shows it to contain some iron and a small amount of 

 nickel in addition to silica. These structures suggest that there was 

 a pool of molten and boiling silica (the silica vapor causing the 

 highly cellular structure), and that a rain of molten silica was shot 

 out from the craters through an atmosphere of silica, iron, and nickel 



" Geogr. .loiirn.. vol. 81, January 19:>3 ; and bis book, The Empty Quarter, Constable 

 & Co., London, 1933. 



