36 Proceedings of the Royal Society of Victoria. 



induce the shape of a drop of water, or fluid lead descending from 

 a tower or into a shaft, forming shot globules, but modified by 

 the influence of atmospheric resistance. I have also assumed 

 that rotation took place, simply because it seemed the most 

 reasonable view to adopt on account of variance exhiVjited in 

 some specimens, and that a simple progressive motion does not 

 seem compatible with the elongated form with contracted centre. 

 Even in the button-shaped obsidianite, the flat grooving shows at 

 times a distinct spiral, as if it had been turned on a lathe, and 

 in one specimen (Fig. 6, PI. III.), the upper surface is scored with 

 fine circular lines, or what is probably a fluxion structure due to 

 rotation about a vertical axis. Other specimens have the pits on 

 that surface arranged in a similar manner. I do not therefore 

 think that the causes which induce the spherical form of what 

 could have entirely prevailed, and certainly I have not seen any 

 obsidianite bearing a resemblance to the form of a bomb which 

 has, according to Professor Stelzner, had a simple progressive 

 motion. 



The pittings, which are so characteristic of obsidianites, afibrd 

 interesting matter for investigation. If they were produced at 

 the moment of their origin, before the present forms were attained, 

 which we suppose to be due to their passage through the air 

 whilst in a molten state, it might naturally be expected that they 

 would have thereby suffered elongation and contortion. In the 

 hollow specimen and some of the others to a certain extent, this 

 seems to have taken place when an apparent flow of the material 

 has elongated and drawn the pits into groups and bands so 

 closely crowded as to almost blend into one another. Also on 

 some of the button-shaped obsidianites on the smooth gi'ooved 

 surface no pitting appears, the conclusion being that they were 

 smoothed out or obliterated by the friction of the air against the 

 rapidly moving object. On the contrary, however, other speci- 

 mens exhibit the pittings equally distributed over the surface, 

 and show no indication whatever of alteration from the regular 

 half sphere, and in one instance two isolated pits of undisturbed 

 form are present on the rim of a most perfect button-shaped 

 specimen. They look very much as if they were caused by some 

 small spherical body falling on the soft material. It is also 

 observed that the grouping which is present in the hollow speci- 



