206 Dr. F. P. Mueller — Tektite from British Borneo. 



critical area (see Map, Fig. 1, p. 201). If such capture took place in 

 Miocene times, it would appear to have been due to the hollow- 

 complementary to the ripple-crest which was at that time farther 

 north-eastwards. Although the region was affected by widespread 

 movements in Pliocene times, the crest may have tended to return 

 south-westwards again as indicated first by the Crag outcrop and 

 later (and farther south-westwards) by the rejuvenation due to 

 uplift. 



What was the impelling force driving the ripple so persistently 

 north-eastwards, where did it originate, what are its effects outside 

 this area, and what is the meaning of the rebound ? These are 

 theoretical considerations upon which it is better perhaps not to 

 speculate at present, but which may open up fresh questions and 

 lead to further investigation and accumulation of evidence. 



Finally, it should be stated that the problem of attempting to 

 prove the existence of an unstable axis was never embarked upon. 

 The facts obtained in the course of working out other problems on 

 each of the East Anglian deposits gradually fell into line. 



I 



III. — Tektite from British Borneo. 



By Dr. F. P. Mueller, Basle (Switzerland). 



T is well known that in various regions of Europe, Asia, and 

 Australia dark pieces of glass are found which, in view of their 

 peculiar shape and sculpturing, have attracted the attention of observers 

 for a good many years. The name of obsidianite was given to these 

 objects by 11. H. "Walcott. It expresses their resemblance in 

 petrographic nature to obsidian. 



Obsidianites are found in widely separated regions. It is evident 

 from their physical and chemical properties that they belong to one 

 petrographic class. However much they resemble one another there 

 are points characterizing the specimens of each region. For this 

 reason F. E. Suess has classified the obsidianites according to the main 

 places of their occurrence, as Moldavites, Billitomtes, Australites, and 

 Queenstoivnites. In this view the origin of obsidianites is considered 

 as a cosmic one, and excludes any comparison between them and 

 obsidian ; as an alternative the same author has chosen the name of 

 tektite (tj/zcto?, molten), which he thinks is less open to objection. 



The origin of tektites has been dealt with in numerous publications. 

 It is their occurrence upon or in later deposits remote from recent 

 volcanoes and manufactories, and their shape and sculpturing, that 

 have been considered as the result of their cosmic source. Many 

 doubts have been expressed as to these points. The extreme 

 discordance between the petrographic characters of meteorites and 

 tektites, chemically belonging each to the opposite ends of the rock 

 series, was supposed to prove the impossibility of a meteoric origin 

 for the tektites. Yet it is evident from a study of the analyses that' 

 there is no agreement between the chemical composition of tektites 

 and of any similar known terrestrial rocks. It will therefore be 

 hardly possible to think of any other than a cosmic origin for them. 



