284 F. E. AVRIGHT OBSIDIAN FROM ICELAND 



(3 ) The moldavites are raeteoritic in origin. Tn the case of meteorites 

 the conditions are nnique. Tlie meteor enters the earth's atmosphere as 

 a very cold liody. The frictional resistance of the atmosphere very 

 quickly raises the temperature of the exposed surface of the meteorite to 

 the melting region. Such melted portions are then brushed ofP, Avith the 

 result that only a thin crust of the molten matter is left on the meteorites 

 Avhen they reach the earth's surface. The period of flight through the 

 atmosphere is of such short duration that the center of the meteorite does 

 not become appreciably heated. According to Professor Merrill, to whom 

 the writer is indebted for a statement of the conditions which obtain 

 during the fall of a meteorite, the only recorded instance in which a 

 meteorite was touched immediately after it had reached the earth's sur- 

 face showed that the meteorite was "stone cold." The result of such con- 

 ditions of flight and local surficial heating is intense local strain analogous 

 to the strains set up on inserting a large piece of glass into a hot Bunsen 

 flame. The glass fragment commonly cracks into pieces, or small chips 

 spall oif analogous to exfoliation shells on rocks exposed to sudden 

 changes in temperature. The outer forms of stony meteorites indicate 

 that they have been subdivided in this manner. 



The distribution of the strains set up under such conditions can be 

 readily obtained by inserting the edge of a cover glass or object glass into 

 a Bunsen burner. If care be taken to avoid fracturing, the edge of the 

 glass plate melts, while the center and opposite edge are still cold. Ex- 

 amination of the plate after cooling shows the presence of a very narrow 

 marginal band under intense compressional strain, which decreases in the 

 direction of the center and passes through a neutral line into a zone of 

 tensional strain, which soon reaches a maximum and then diminishes 

 gradually and practically disappears near the center. The glass plate 

 usually breaks asunder later near the line of maximal tensional strain. 



Examination of moldavite specimens from Bohemia^" showed a distri- 

 bution of strain identical with that described above for conditions of 

 cooling postulated under case 2, namely, those of a highly heated or 

 molten mass of glass chilled rapidly. The small etched obsidian frag- 

 ments from Hrafntinnuhryggur (specimen 88435) exhibit the same dis- 

 tribution of strain. In the moldavite specimens the strain is distributed 

 in such a manner as to indicate that they are not fragments of a large 

 mass of annealed glass (obsidian or artificial glass) or single meteorites, 

 but rather fragments resembling in character the spatters or splashes of 

 molten obsidian described above. It should be noted, however, that the 

 meteoritic origin of the moldavites is not absolutely disproved, for it is 



™ The writer is indebted to Professor Merrill for the loau of these specimens. 



