The Causes and Phenomena of Earthquakes. 65 



of the water sometimes precedes a storm, owing to the undu- 

 lations affecting the bottom of the sea ; and this was seen at 

 Bermuda in 1831, the day before the hurricane arrived. 



The occurrence of meteoric phenomena off the coast of New 

 South Wales on the night- of 17-I8th August, and the sudden 

 violent south-east gale of the 19th, prove that there was an aerial 

 as well as oceanic disturbance about this period. The death of a 

 steersman in a vessel off Crowdy Head on the 17th, by a meteoric 

 explosion is an extraordinary fact. Respecting such storms there 

 are recorded many coincidences with earthquakes ; and such was 

 the case at Tobago, where the violent hurricane of llth October, 

 1846, was preceded by a shock. A meteor was observed at 

 "Wood's Point, (Victoria) on 20th August, falling during a heavy 

 rain, and succeeded by a shock of earthquake. 



All doubt as to the character of our recent marine disturbances, 

 was, however, removed by the arrival of the Kaikoura, from Pan- 

 ama, on the 23rd August, and by her we learn, that the ocean 

 disturbance was felt also on the east coast of New Zealand, on 

 the 15th, 16th, and 17th, and that a shock of earthquake was also 

 felt along the east coast and at Nelson and Wellington, on the 

 17th. 



It is certain, therefore, the ocean was affected at the same 

 time, at opposite points, in an area of at least 1,300,000 square 

 miles. This very fact destroys all idea of aerial disturbance 

 having been the motive power, as in that case the motions would 

 not have been simultaneous, but progressive. The shock was felt 

 from Lyttelton to Napier ; and at the former place a ship lifted 

 on and off the pier, having been first left dry by recession of the 

 water Further particulars will be found in my catalogue. 



To return now to the main topic, supposing a shock to originate 

 in the expansion of gases on the surface of a molten fluid, there 

 must in that fluid be a greater velocity than in a vibratory wave 

 of compression in water, which is about 4800 feet per second. 

 On the supposition of a thin flexible crust, a small force might 

 produce considerable effect, but to produce elevation in thick 

 compact strata, a long and continuous force producing tension 

 approaching to dislocation would be required. 



In the quotations of time of the shocks already mentioned 

 there may be some error ; for no instrument has ever yet been 

 invented to determine such a fact accurately. Moreover, where 

 a shock has to traverse strata of different conditions of structure 

 and flexibility, the times of propagation must vary in each. 



I have dwelt long on the mathematical theory, because it is 

 that which appears to have in it the greater elements of certainty, 

 and because we cannot solve the difficulties presented to us 

 without consideration of the laws that regulate motions in solids 

 and fluids, and which belong to what may be called the dynamics and 



