Ohsldian Borahs in Atistralia. 37 



men has been sharply limited by the peripheral ridge, and the 

 pits on the corrugated portion are not aifected in the same way. 

 Besides this, the occurrence of pits within others suggests a 

 doubt as to whether they were originated at one time. Again, 

 in Fig. 6, PL III., the surface has the appearance of being com- 

 pletely covered with a black coating, as if it has been frosted, but 

 on close examination it is seen to consist of innumerable pits, so 

 closely aggregated as to pi^esent no perfect forms. This structure 

 resembles on a small scale the pittings or thumb marks, so well 

 known as characteristic of meteorites. It is more than likely, 

 therefore, that these pits result from a cause acting throughout 

 the time they were in a molten or, at least, a soft condition, even 

 after their ultimate form was assumed, and that they were not 

 due to decomposing agencies at a later period. The corrugations, 

 which, as far as can be ascertained locally, bear a resemblance to 

 the ridges and furrows of meteorites, are always present on the 

 sides of obsidianites, and are approximately vertical in their 

 direction. If they are due to a similar cause, that of a flow of 

 the melted material from front to back, then they could not have 

 been formed by a rapid descent or ascent. Had this been so, 

 they would have been horizontal or otherwise ; they would 

 simply be rims, because this is practically how these are supposed 

 to have been formed. It appears, therefore, under this assump- 

 tion, that they resulted in all proV)ability in a rapid horizontal 

 rotation. Some of the button specimens have a slightly wrinkled 

 appearance on the outside of the rim, as if it were indicative of 

 previous corrugation, which has been partially overcome and 

 inoditied by the friction due to vertical flight. 



The markings on the obsidianites from Central Australia, 

 which were kindly lent to me by Mr. J. A. Watt for examina- 

 tion, differ both in form and distribution from the pittings, and 

 are probably due to a different cause. Their entire surface is 

 completely scored with these small marks, and their general 

 form shows signs of erosion, as mentioned by Messrs. Tate and 

 Watt. The view that these surface markings are secondary is 

 strengthened by the fact that some of the specimens have every 

 appearance of being fractured either by their fall on earth or 

 contact with other substances ; but the fractured surface differs 

 ill no way from the remainder. If they ai'e secondary, then a 



