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BULLETIN 149, UNITED STATES NATIONAL MUSEUM 



oval forms without distinct surface markings. Those of Moldavia 

 are of a green color, of extremely irregular forms, and gashed and 

 impressed in a manner to suggest they may, in plastic condition, have 

 been subject to mastication like a mass of chewing gum. The forms 

 from the island of Billiton are the most singular and unaccountable of 

 all. Like those of Australia, they are of a dense, opaque glass, their 

 distinguishing character being as in the last case, the peculiar surface 

 markings. Chemically, as shown in the accompanying table, they 

 average a trifle higher in silica, calcium, and ferric oxide than the 

 ordinary obsidian, and are poorer in alkalies. Their resemblance to 

 known meteorities in composition is remote. Each locality yields 

 its own peculiar forms, though all are grouped under the general 

 name of "tektite." In no instance have there as yet been dis- 

 covered facts relative to their occurrence such as can give a clue to 

 their origin. By some they are firmly believed to be glassy meteor- 

 ites. How far the difficulty of accounting for them otherwise may 

 have had influence in the formation of such an opinion the writer is 

 not prepared to say. 



Analyses of tektites 



I. Obsidian pebble. Colombia. Analyst, J. E. Whitfield. 

 II. Obsidianite. Upper Weld, Tasmania. Analyst, W. F. Hillebrand. 



III. Obsidianite. Near Hamilton, Victoria. Analyst, O. Ampl. 



IV. Moldavite. Tribitsch, Boliemia. 



COMBUSTIBLE METEORITES 



The fact that there is so complete a lack of coordination between 

 the periodic meteoric showers and the fall of meteorites has more 

 than once suggested the possibility that the materials of the first 

 mentioned might be of an easily combustible nature, so that they v/ ere 

 consumed in their passage through the atmosphere, while only those 

 which were composed chiefly of metal or silicate materials survive, 

 and this only in part. The fact, too, that there is known a group of 

 carbonaceous meteorites (Orgueil, etc.) containing in certain cases as 

 high as 14 per cent of volatile matter, gives the suggestion a certain 

 degree of probability. In this connection, then, it may be well to 



