6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I43 



used in making the photomicrographs (pi. 4). Figure 1, A, is of a 

 section from the flat end of the Georgia tektite specimen (pi. 1, A). 

 The slice from which figure 1, B, was prepared was taken several milli- 

 meters in from the left broken edge of the Martha's Vineyard speci- 

 men positioned as in plate 1, B, extending approximately two-thirds 

 of the way into the specimen and parallel to that edge. This relation- 

 ship of surface to flow structure is unusual for tektites in general 

 (Barnes, 1940; Baker, 1959). 



The present external surfaces of these specimens are essentially 

 secondary features due largely to chemical etching. Indeterminant fac- 

 tors such as the original shape of the specimen, the susceptibility of its 

 various parts to chemical attack, the nature of the chemical environ- 

 ment and the time through which it has acted, and mechanical effects, 

 combined to produce the present surface features of these tektites. 

 The main surface features, pitting and grooving, have no obvious 

 relation to the internal structure of the material. Tektite surface pits 

 are sometimes referred to as bubble cavities, but it is unlikely that 

 bubbles within the glass were responsible for the pitting on the 

 tektites we studied. It has been mentioned above that the bubbles 

 present in the sections were small and sparsely distributed (pi. 4). 

 Their concentration in the medium and their individual diameters are 

 both minute when compared to the surface pits. 



The internal flow structure, however, is related directly to delicate 

 striae that are readily observable as a secondary surface feature on 

 these specimens. The striae frequently occur where the flow structure 

 is truncated by the specimen surface and undoubtedly result from 

 slight differences in susceptibility to chemical attack. The left-hand 

 piece of the Empire, Ga., tektite shown in plate 2, A, exhibits striation 

 which is of particular interest because it indicates the extent to which 

 flow structure conforms to the surface of the specimen. The striae 

 follow the edge of the specimen and suggest that the flow structure pat- 

 tern based on the section (fig. 1, A) holds in a general way for the 

 complete specimen. The arrows in figure 1, A, indicate areas where 

 the U-shaped striae on the surface of the specimen (fig. 1, A) 

 terminate. 



Striae are obvious on the surfaces of the Martha's Vineyard tektite 

 (pi. 3, A and B) and especially on the serrated edge (pi. 3, C). The 

 concentric external pattern is consistent with the flow structure illus- 

 trated from the section (fig. 1, B). The second Empire, Ga., tektite 

 (pi. 5) is a striking example of surface expression of internal struc- 

 ture. The more irregular pattern on this tektite probably indicates 

 a more contorted flow structure. Surface striation of this type 



