ON SEISMOLOGICAL INVESTIGATION. 18T 



Mr. W. G. Forster, in his paper on ' Earthquake Origin,' ' from which we 

 learn that cables have, after their interruptions, been recovered from 

 which the gutta-percha had been melted— probably by water at a high 

 temperature. The cables referred to are near the Lipari Islands and 

 between Java and Australia. 



Some idea of the frequency of earthquakes and volcanic shocks origin- 

 ating in the ocean may be obtained from a paper by Dr. Emil Rudolph.^ 

 From his descriptions, which are derived from the catalogues of Perrey^ 

 Mallet, the archives of the London Meteorological Office, &c., the follow- 

 ing table has been drawn up : — • 



North Atlantic, 1724-1886 .... 



Azores, 1843-1884 



Cape Verde Islands, 1854-1883 . 



St. Paul's, 1845-1886 . ... 



Equatorial Atlantic, 1747-1878 . 



West Indies, Leeward Islands, 1839-1886 . 



South Atlantic, 1616-1875 .... 



West Mediterranean, 1724-1865 . 



East Mediterranean, 1820-1886 . 



Gulf of Mexico and Caribbean Sea, 1751-1884 



Indian Ocean, 1818-1883 .... 



North Pacific, east side, 1790-1885 



South Pacific, east side, 1687-1885 



North Pacific, west side, 1773-1681 . 



South Pacific, west side, 1643-1885 . 



East Indian Archipelago, 1796-1883 . 



Total . . 333 



The records generally are more frequent as we approach modern times, 

 and, to some extent, for those seas and oceans where there have been the 

 greatest number of observers. Dr. Rudolph regards all his records as 

 referring to shocks of volcanic origin, and, if they agree with his definition 

 of Seebeben, which are shakings originating in the ocean and propagated 

 as elastic waves, we concur in his views. 



2. Sedimentation and Erosion, 



This section of the paper is a consideration of conditions which lead to 

 the formation of sub-oceanic surfaces of instability which may yield by the 

 continuation of the operations by which they are produced, or by seismic 

 or volcanic actions. 



The first fact to be noticed is that the materials resulting from marine 

 denudation round coast-lines and subaerial denudation of continental 

 areas are almost entirely deposited in the ocean, upon an area which is- 

 relatively -small as compared with that from which they were derived, and 

 therefore the rate of growth on littoral areas per superficial unit is on the 

 average greater than the rate of loss similarly estimated on continents. 

 We know from soundings that the materials derived from land are not 

 always deposited to form a gently sloping submarine plain, but often to 

 form surfaces with steep slopes. Thus, for example, the line of the CongO' 

 continued seawards is represented by a gully the sides of which have 

 apparently been built up as a submarine levde. Materials thus accumu- 

 lated under the influence of gravity and hydrodynamic action apparently 



' Trans. Seis. Soc, vol. xv. p. 73. ^ See p. 183. 



