268 



evidence of alteration in the level of the land. This, how- 

 ever, is always very difficult to determine even on the sea 

 shore, while inland it is very unlikely indeed to be noticed if 

 slight. It may be well to allude here to the idea that the 

 source of disturbance was or is near New Zealand. This 

 seems to be very unlikely, as most of the shocks are only felt 

 over a small area, and in the case of the severer ones in which 

 there are discrepancies in time, besides the sources of error 

 already mentioned, it must be remembered that the "co- 

 seismic lines" are not likely to be true circles, since, in 

 the case of earthquakes in Europe, a shock has been known 

 to travel twice as fast in one direction as it does in the 

 opposite, and it is well known that in South America most of 

 the earthquakes are felt over much longer distances parallel 

 to the chain of the Andes than transverse to that line. 

 Besides this, we have reports from New Zealand that few 

 shocks or tremors have been felt there recently. 



It is probably known to most here that Tasmania is united 

 to Australia by a submarine plateau, and that the water is 

 never deeper than 100 fathoms. Beyond the East Coast of 

 Tasmania and Australia the sea bottom rapidly sinks to a 

 depth of over 2,000 fathoms, and continues deep until ap- 

 proaching the coast of New Zealand, so that a deep trough 

 divides us from New Zealaad, and earthquake shocks origi- 

 nating there would have to be at a considerable depth to be 

 strongly felt here. 



We may therefore claim, I think, to produce our own 

 earthquakes, and not to be dej^endent for the supply on New 

 Zealand. 



As to whether we shall be favoured with a really serious 

 and interesting shock, of course no one can say. But while 

 it would be foolish to deny the possibility of its occurrence 

 here, as it would be in any other part of the world, it would 

 be equally unj)hilosophical to imagine that, because we have 

 had many slight shocks, we shall therefore have a great one, 

 since it is well known that really severe shocks, which are 

 never common, while they are sometimes preceded by slight 

 ones, in many cases occur without any warning at all. The 

 great earthquake of Lisbon of 1755 is a case in point, and 

 many others might be mentioned. Many places also, such as 

 Comrie, in Perthshire, Scotland, have very many slight 

 shocks, but have never been known to experience a serious 

 one. 



The great interest, indeed, of our earthquakes, in a scientific 

 point of view, is the occurrence of such a large number of 

 slight shocks close together in a country where they were 

 previously very rare. 



About the causes which produce earthquakes, but little 



