1 88 PHYSIOGRAPHY. [chap. 



impulse may be transmitted through the earth to an enor- 

 mous distance ; the great earthquake which destroyed 

 Lisbon in 1755, having made itself felt, directly or indirectly, 

 on the waters of Loch Lomond in Scotland. If the centre 

 of disturbance is near the sea, the water is affected even 

 more than the land, and the water-waves may be far more 

 destructive than the earth-waves. News has recently reached 

 this country of the terrible devastation wrought by the great 

 tidal wave which followed the earthquake at Lima, Arica, 

 Iquique and other points of the coast of South America 

 in May, 1877. 



A good deal of attention has been paid by Mr. R. Mallet 

 to the study of earthquake phenomena, or Seismology,'^ and 

 he is led to conclude that the origin of the disturbance is 

 usually not deep-seated in the interior of the earth, probably 

 never exceeding a depth of thirty miles ; while in many 

 cases, it is certainly much less. Thus he ascertained that 

 the great Neapolitan shock of 1857 had its origin at a 

 depth of only eight or nine miles beneath the surface. Dr. 

 Oldham has since found that a great earthquake at Cachar, 

 in India, in 1869, had its focus, or centre of impulse, at a 

 depth of about thirty miles. 



Although earthquake-shocks are happily of rare occur- 

 rence in this country, it must be remembered that, in many 

 parts of the world, they are by no means rare phenomena; 

 and, probably, it is not overstating the case to say that earth- 

 quake shocks occur, on an average, about three times a 

 week. During the year 1876, for example, no fewer than 

 104 earthquakes are recorded in Professor Fuchs's Annual 

 Report; and, in the preceding year, as many as 100 days 

 were marked by the occurrence of shocks. But, in addition 

 to these, there are no doubt many slight disturbances, in 

 1 Sdsmology, from <re«r/i3s, seismos, a shock or earthquake. 



