8 JOURNAL OF SCIENCE. 
of a rock in which the tension had been gradually increased, but 
we cannot well imagine a large explosion being followed by 
several smaller ones. Again, the movements of the land which 
often accompany earthquakes are not in the least like the move- 
ments caused by the explosion of a mine, but are much more 
probably due to the movements of the rocks which would often 
necessarily follow the rupture. 
In order to make this appear more plain, a possible hypothesis 
as to the origin of the earthquakes in New Zealand may be ha- 
zarded. It was shown in an article published in the Vew Zealand 
Magazine for October, 1877, that there are three principal seismic 
regions in New Zealand, Ist. in the neighbourhood of Cook’s 
Straits; 2nd, in the Hot Lake district, north west of Lake 
Taupo; and 3rd in Otago. The strongest and most widely-spread 
earthquakes occur in the first region, while all those in the second 
region are small and local. Now there is some geological evi- 
dence, not undisputed however, to show that the elevation of New 
Zealand has been much more rapid in the centre of the North 
Island, and in the southern and central portion of the South 
Island than in the neighbourhood of Cook’s Straits, where, indeed, 
as at Nelson, there may have been depression. If this is really 
the case, then the forces at work on this part of the earth’s 
crust must be gradually folding up the rocks of New Zealand 
into a flattened M, the central depression of which lies in Cook’s 
Straits. In this way tensions might be produced at each of the 
three bends, the relief of which, by fracture causes the earth- 
quakes. The central region of bending, under Cook’s Straits, 
would lie deeper than the other two, and would thus account for 
the earthquakes of this region being more severe than those of 
any other part of New Zealand. But whether this hypothesis 
be correct or not, if the earthquakes of New Zealand 
are caused by fractures taking place in the underlying rocks, 
which fractures temporarily relieve the gradually accumulating 
tensions, it is evident that they belong to a part of the mechanism 
of the earth which is not likely to change soon; that, however 
quiet things may appear on the surface, changes are taking e place 
below which must, gradually but surely, lead to a repetition of 
the same effects ; but after how long an interval no one can say. 
Whether these earthquakes are or are not caused by fractures of 
the rocks could Sea be determined ay observation. 
Note.—A description by an eye-witness ‘oe late Hon. H. S. Chapman) of the 
earthquake that took place in Wellington in 1848 will be found in the Westminster 
Review for July 1849. A record of the principal phenomena connected with the 
earthquake of 1855 will be found in Sir C, Lyell’s ‘‘ Principles of Geology.” 
