340 Transactions. — Geology. 



near it, and the first fissure made available for the escape of 

 steam from the heated beds passed through one side of the 

 mountain. (It is not uuUkely that the mountain was plentifully 

 fissured and creviced beforehand.) On a way being opened for 

 the escape of the steam, it was promptly taken advantage of. 

 For some time the force of the steam would be largely employed 

 in tearing away the sides of and enlarging the vent , the product 

 of this action being the larger stones described as underl}dng 

 the sand and dust on and near the mountain. All this time, as 

 afterwards during the continuance of the eruption, the steam in 

 escaping from the heated rock (which was possibly crushed, cer- 

 tainly weakened in its cohesion,) would tear off and crumble off 

 its " face," and carry the fi-agments out through the fissure, to 

 scatter them to the winds. 



There is no evidence, I understand, that any portion of the 

 ejecta had been fused, but the fineness of the great mass indi- 

 cates that the rock from which it was derived was very 

 thoroughly crushed by the movement which heated it, by the 

 escaping steam tearing it to pieces, or by both actions together. 



The subterranean rock movements continued, as indicated 

 by continued earthquakes ; the fissure through the upper beds 

 was extended, and a second set of eruptions set up further south, 

 the subterranean action being similar to the first. In connec- 

 tion with this second eruption, I should like to offer a suggestion 

 as to the cause of certain noises that have been described as 

 "horrible roarings," that ceased after a time, by those who 

 were unfortunate enough to be in Wairoa on that memorable 

 night. These may have been common volcanic sounds, but 

 they may not. One of the chief centres of the second eruption 

 was Lake Eotomahana, from the bed of which very copious 

 ejections took place. Now one of the most horrible noises I 

 ever heard is that caused by the condensation of steam within 

 a body of water, as when a locomotive-driver turns a steam jet 

 into his water-tank — a measure of economy when his steam is 

 blowing off". Exchange the locomotive-tank for a lake, or 

 quarter-inch pipe for an aperture possibly some yards in area, 

 and 1501bs. pressure for, say, l,0001bs., and one can imagine a 

 cause for the " horrible roarings " heard at Wairoa. This noise 

 •would cease as soon as the escaping steam had carried up 

 material enough to construct a cone, or cones, to the surface of 

 the lake. A great deal of the water which went to make the 

 mud that overwhelmed Wairoa may have been carried into the 

 air as spray by the powerful steam jets that played through the 

 lake. At any rate, a considerable quantity of water must have 

 been carried up in this way. 



An interesting question is : What is the nett result of the 

 eruption in the nether regions ? Has a cavernous space been 

 formed by the removal ot so much solid material ? I think not. 



