278 Transactions. — Geology. 



None of the hot springs were permanently altered, although 

 those on Hannier Phxms were much agitated, became muddy, 

 and emitted more gas, but with no extra flow of water. By 

 the 5th September they were merely discoloured, and they 

 gradually got quite clear again. Sulphuretted hydrogen 

 escaped from the ground in many places near the hot springs ; 

 and it was reported that it escaped from other places on the 

 plain, but there is no evidence of this. A small opening was 

 made close to the swimming-bath, which spouted out mud 

 and gas, with very little water, for the three days that the 

 ground was in constant movement. 



All these phenomena appear to me to be secondary effects 

 of the earthquake — that is, they were not the cause of the 

 shock, but were produced by the reaction of the earth-wave 

 in its propagation through the earth. Fissures which are 

 more or less parallel to some superficial feature of the surface 

 must almost certainly be themselves superficial ; and fissures 

 which are confined to alluvial deposits must almost certainly 

 have originated in those deposits. They can, I think, all be 

 explained by the prmciples laid down by Oldham and Mallet 

 in their paper on the earthquake in Cachar of 1869. '•■ 



Pkobable Position of Epicentkum. 



There are three different kinds of evidence which will 

 help us to find the probable position and shaj)e of the epi- 

 centrum : — 



(1.) The intensity of the shock in different places. 



(2.) The direction of the shock in different places. 



(3.) The time the shock was felt at different places. 



The first kind of evidence will give us true results so far 

 as it goes, and when an earthquake has originated in a well- 

 populated and civilised country this method can be relied on ; 

 but when an earthquake originates under the sea or in a 

 thinly-inhabited district it cannot lead to very accurate 

 results. The second and third kinds of evidence are liable 

 to many sources of error; but if all erroneous observations 

 could be eliminated, the remainder would give a much closer 

 approximation to the truth than can, in the cases supposed, 

 be got from the first kind of evidence. 



In our case the earthquake originated in a district not 

 only very thinly populated, but one very difficult to examine — 

 so much so that the only accurate observations that have 

 been made are along one line — from west to east ; all the 

 country to the north, west, and south of the place of origin 

 being as yet unexamined. This being so, it is obvious that 



* "Quarterly Journal of the Geological Society of London," vol. 

 xxviii., p. 255, 



