Wellington Philosophical Society. 451 



natural phenomena, required to be classified. Until within the last few 

 years this had been attempted only by theories of their origin. What is 

 required is accurate description and record, so that the varieties may be 

 differentiated. A classification somewhat of the following nature might be 

 adopted : Thus, in the first place, earthquakes and volcanic action are popu- 

 larly connected, and their relation is easily understood, but applies only in 

 a comparatively few cases, as there are many other kinds of earthquakes 

 that do not appear to be connected with volcanoes. Secondly, we may 

 have a primary impulse radiated from a deep-seated focus of small dia- 

 meter — of which the Charleston earthquake of 1st September, 18S6, was a 

 marked example. This spread 1,000 miles in all directions from a focus 12 

 miles beneath the surface. The area within which the vertical displace- 

 ments exceeded the lateral was 26 by 18 miles, but the focal points were 

 along a curved line only 12 miles in length. Even in this earthquake we 

 thus see a tendency to a longitudinal extension of the focus, but the impulse 

 that caused the primary shock was simultaneous. This leads to the next 

 class of heavy earthquake shocks that have great longitudinal extension, and 

 which generate fresh impulses successively as they are propagated through a 

 tract of country in which the undulations meet with strata in a condition of 

 stress. It is to this class we must refer the only two great earthquakes that 

 have been recorded in New Zealand, as they were propagated from N.E. to 

 S.W. for a distance of at least 800 miles, while the lateral propagation was not 

 more than 100 miles to the N.W. or S.E. A short abstract was given of the 

 principal features of these two earthquakes, which occurred in October, 1818, 

 and January, 1855, from the descriptions published at the time by Sir 

 William Fitzherbert, and the late Judge Chapman. Lastly, we have slight 

 tremors that frequently reach us, evidently from a great distance to the 

 S.E., and which, except where they locally encounter superficial conditions 

 of instability, do no material damage. They are widespread ; and, if the 

 undulations are circular, they must have an enormous diameter, as they 

 affect New Zealand nearly as if they were straight lines. 



The early records are necessarily very incomplete, and commence with 

 the earthquake felt near D'Urville Island by Captain Furneaux on the 11th 

 May, 1773. Subsequently only prominent shocks are referred to, until from 

 the beginning of 1816 to October, 1848, when the shocks felt in Wellington 

 were recorded. From that date until 1868 the record is very imperfect ; but 

 since 1868, when the present Meteorological Department was organized, and 

 the telegraph brought into operation, the record has been tolerably complete 

 for the whole Colony. The earthquakes during this latter twenty years 

 have therefore been scheduled, the Colony being divided into six districts, 

 each having a characteristic structural peculiarity, as shown on the map 

 exhibited. An analysis of this schedule showed that during the period 537 

 earthquakes have been recorded : of which only 2 were recorded in the 

 northern district of Auckland ; 184 in the central district of the North 

 Island ; 183 on the east coast of the North Island ; 88 on the west coast of 

 the South Island ; 98 on the east coast ; and 30 in the extreme south. But 

 of the above number 142 were felt only in the middle section of the North 

 Island, between the South Taranaki Bight and the Bay of Plenty ; 147 only 

 in the district between the East Cape and Wellington; and 115 were con- 

 fined to the east and south coast of the South Island. Of the whole number, 

 only 7 could be identified as having been felt in places outside the Colony. 

 In conclusion, a short reference was made to the modern views as to the 

 causes of earthquakes, and especially to the important bearing of a recent 

 paper by Mr. Autray Strachan, F.G.S., regarding the destructive effects of 

 explosions from " slickensides," or smooth surfaces formed by motion along 

 deep-seated faults, when these faults have been brought within reach of 

 the miner's pick by the elevation of the land. It appears that these smooth- 

 faulted surfaces are in a state of intense molecular tension, probably 

 acquired through slight movements when under intense pressure at pro- 



