ON SEISMOLOGICAL INVESTIGATION. 



203 



All that it is expected to find is that a certain, and probably a 

 small, proportion of these interruptions may correspond in time with 

 seismic disturbances ; and, because we know that certain cables have 

 been lost by landslips and dislocations accompanying earthquake-move- 

 ment, it is to be hoped that the expectation may be regarded as a 

 reasonable conjecture. 



An Attempt to estimate the Frequency of Submarine Dislocations. — 

 If it can be assumed that the majority of cable-interruptions are due to 

 submarine displacements, and not to faults inherent in themselves (which 

 are comparatively of rare occurrence), the swaying of suspended sections 

 under the influence of waves and currents, the movements of marine 

 creatures, the boring of a teredo, and other exceptional causes, tlien the 

 tables which have been given of cable fractures will give some idea of the 

 frequency of such displacements. Because the list of interruptions for 

 a number of the lines mentioned are imperfect, and because each cable 

 follows a path carefully chosen as not being likely to suffer from sub- 

 marine disturbance, the frequency of dislocation derived from such an 

 assumption is more likely to be a minimum than a maximum. From the 

 known number of interruptions which have occurred on sections of given 

 length in a given number of years, the following table of dislocation 

 frequency per mile of coast per year has been computed. 



