424 Transactions. — Geology. 



to the axis of folding of the older Pliocene rocks in Hawke's 

 Bay, and to the general axis of New Zealand. They are also 

 just on the outside of the sloping plateau which about 

 250 miles to the E.S.E. rises above the sea as the Chatham 

 Islands. Between this line of origins and the south-east 

 coast of the North Island is a trough in the ocean-bed with a 

 depth of 1,000 to 2,000 fathoms (AA). 



It is probable that the earthquake of the 9th August was 

 due to sudden slipping along a fault-plane, or other similar 

 movement that occurred in the process of the " repacking " of 

 the deeper rocks, consequent upon the continuance of the fold- 

 ing which the geological evidence shows to have been going 

 on for many ages. 



The maximum displacement or amplitude of an earth- 

 particle may be calculated from the other elements of the 

 earthquake : the data in this case give 2-2-5 mm. as the 

 maximum horizonal displacement ; the vertical displacement 

 would consequently be not greater than i mm. or J$ in. 



The isoseismals, or lines of equal earthquake-intensity, 

 marked on the map confirm in a general way the con- 

 clusions already established in regard to the region of 

 disturbance. 



[I am indebted for valuable observations and notes of the 

 earthquake to the Secretary of the Post and Telegraph 

 Department and his officers, especially to Mr. Keys of Napier, 

 and to many private persons, the careful notes collected by 

 Mr. B. P. Soundy, of Dannevirke North School, being of 

 great interest.] 



Akt. XLVI. — The Path of Earthquake -waves through the 



Earth.-'- 



By George Hogben, M.A. 



[Read before the Wellington Philosophical Society, November, 1904.~\ 



Plate XXXIII. 



As it has been stated that the apparently high speed of the 

 preliminary tremors in large earthquakes is to be accounted 



* Since writing this paper I have received from the Earthquake 

 Investigation Committee of Japan a copy of a paper on the same subject 

 by Mr. Imamura, of the Hongo Observatory, Tokyo, in which tho writer 

 arrives at the same conclusion from calculations based on nineteen severe 

 earthquakes recorded at all the chief seismological stations of the world. 

 My paper was written ten months before the receipt of Mr. Imamura's 



