EXPLOSIVE OR BOOMING NOISES IN CENTRAL AUSTRALIA. 191 



that although it is sometimes louder than at others, yet it 

 is never near, always distant. I have no doubt but that 

 some time or other the natural cause of it will be discovered, 

 but I have never yet heard the phenomenon explained." 



Mr. D. G. Stead has kindly forwarded me the following 

 note on the occurrence of these sounds in western New 

 South Wales. His suggestion as to their cause is of much 

 interest. "In regard to mysterious rumbling or explosive 

 sounds: — When I was on the Dry Bogan during August of 

 last year, I stayed for two nights on Mr. Barton's Station 

 at Mooculta. While there, and while I was discussing 

 various natural phenomena with Mr. Reginald Kirk wood, 

 Mr. Barton's manager, the former told me that, not infre- 

 quently, at the end of the very hot days, just about and a 

 little after sundown, were to be heard coming from the 

 direction of Mount Oxley (which I could see from there, 

 and which is distant about fourteen or fifteen miles), 

 rumbling and explosive sounds, sometimes loud, sometimes 

 muffled, according to the state of the atmosphere and the 

 direction of the wind. I suggested that it would probably 

 be caused by bursting rock which had become intensely 

 heated during the day, and was undergoing a rapid cooling 

 process. He agreed that this was extremely probable, but 

 could not say from actual observation. He also told me 

 that the summit of Mount Oxley had numerous peculiar 

 crater-shaped conical depressions ; these were only about 

 the summit. This was most interesting to me, and I 

 specially noted it in my book at the time. Upon making a 

 close enquiry later, I found that similar sounds had been 

 heard coming from Mount Gunnerbooka, which I have also 

 seen, and which is about forty miles S.S.W. from Mount 

 Oxley. Now both of these short ranges stand up like islands 

 in a veritable i ocean ' of plain country, the radiation from 

 which must be enormous." 



