506 Transactions. 



folding of the strata near the junction of the land-surface and 

 the ocean-bed, which may continue until fracture takes place, 

 the strata on the land side moving up, and those on the ocean 

 side moving down. The displacement of the strata will form 

 a normal fault. After the fracture the two faces of the strata 

 will continue to slip and to slide one over the other so as to 

 increase the amount of displacement. The slipping may go 

 on very gradually, but from time to time sudden slips will 

 probably occur, and these will produce earthquakes. All the 

 recent earthquakes in New Zealand have been followed by 

 other shocks, showing that the slipping of the rocks has con- 

 tinued for some time after the principal shock. Again, as in 

 the case of folding due to cooling, the differences of vertical 

 pressure will induce lateral thrusts, tending to cause " re- 

 versed faults " ; but in this case the tendency will be most 

 marked at a considerable depth below the surface, where the 

 pressures are greatest. Subsequent action may raise the 

 deeper rocks, and reveal faulting that has occurred ages ago. 



The facts in regard to the folding of the crust are not, of 

 course, so simple as they have been stated here ; but, gene- 

 rally speaking, all the movements resulting from unequal 

 vertical and lateral pressures between the rocks may be 

 summed up in the term " repacking." 



The evidence already given is perhaps not sufficient to 

 establish completely the theory that earthquakes generally 

 are connected with fault-movements and similar processes 

 of repacking of the strata, but it makes that theory highly 

 probable. It must be remembered that the value of such evi- 

 dence necessarily depends upon its cumulative weight, and it 

 would be too tedious to give a large mass of evidence of this 

 kind here. Moreover, our knowledge of the position of the geo- 

 logical faults in New Zealand is too limited as yet to prove the 

 theory from New Zealand examples. Dr. Charles Davison, 

 an able British seismologist, has shown in a very careful series 

 of investigations the connection between many British and 

 European earthquakes and known lines of fault. 



A study of the map of the seismic origins in the New Zea- 

 land region (Plate LIV) will strengthen the evidence already 

 given in favour of the theory. Before considering these, it 

 may be as well to name the nearest known origin outside the 

 New Zealand region. 



On the 27th January, 1892, an earthquake of the inten- 

 sity VII-VIII (Rossi-Forel scale) — probably X near the origin 

 — was felt over almost the whole of Tasmania, in Victoria 

 as far west as Melbourne, and in the south-east part of New 

 South Wales, but not in New Zealand. The epicentrum was 



