HuTTON.— T/i<3 Earthquake in the Avuiri. 287 



generally agreed that they came from various directions be- 

 tween west and north ; and they appear to me to proceed 

 from an elongated area some thirty miles in length, between 

 the hot springs in the Hope and the hot springs in Cow 

 Creek, or perhaps from the neighbourhood of these two lo- 

 calities only. 



As a rule the hot springs at Hanmer showed no sympa- 

 thetic action with the noises, the only exception being a 

 sharp boom, like a cannon-shot, at about 11.15 a.m. on the 

 14th September, accompanied by a shock which appeared to 

 be nearly vertical. On this occasion a small quantity of mud 

 and water was thrown from one of the smaller springs only. 



It is difficult to offer a satisfactory explanation of these 

 noises : they have been heard with other earthquakes, but 

 never explained. In our case it is evident that the main 

 earthquake, and all those of the same character that followed 

 it, were quite independent of the cause of the booms. This is 

 shown by the fact that many shocks were not accompanied by 

 any noises, although they were heavier than those following 

 the booms, and also by the heavier shocks of the 1st Septem- 

 ber. 28th September, and 12th October being followed, not pre- 

 ceded, by noises for several days. On the other hand, as the 

 booms were heard before the main earthquake, their origm 

 must be independent of it ; but, as they were far more fre- 

 quent and much louder after the shocks, it is evident that to 

 a large extent they were secondary effects of the earthquake. 



Mr. Mallet suggests that the noises heard after the Cachar 

 earthquakes of 1869 were due to grinding or crushing of rocks ; 

 but this explanation will hardly do for our case, because man>- 

 of the earthquakes were not accompanied by noises, and the 

 booms do not come from the direction of the e]3icei:itrum of 

 the earthquakes. The sounds appear to me to be much more 

 like explosions of steam than crushing of rock ; and this seems 

 to be the only other explanation. There is no direct evidence 

 to show that they are connected in any way with the hot 

 springs, but their geographical distribution strongly suggests 

 it. Hot underground water undoubtedly exists in the district 

 in which the sounds have been heard, and at a comparatively 

 small depth this water may be above the boiling-point, but 

 kept fluid by pressure. If this pressure were removed, part 

 or the whole might flash into steam and produce an explosion 

 which would cause a boom. An earthquake might first com- 

 press this water, and then, on the backward swing of the 

 wave, the pressure would be relieved and explosions take 

 place ; or part of the heated water might be expelled by the 

 shock, which would reduce the pressure on the rest. It 

 seems useless to ofl'er such speculations as these, and I should 

 not have done so if it had not been suggested that these ex- 



