CONTRASTED WITH OTHER FORCES. 65 



those of the Sandwich Islands, nearly seventy in length, 

 and of varying width and thickness, according to the 

 nature of the declivity down which they have flowed. On 

 the whole, there seems no ground for the supposition that 

 vulcanism is now either less extensive or less energetic than 

 in former ages. All that geology perceives is that it has 

 shifted from area to area ; that the old mountains where 

 it once reigned are long since cold and silent; that the 

 secondary hills bear but few traces of its presence; and 

 that now it upheaves along other lines and convulses from 

 newer centres. 



That in vulcanism, as in other cosmical forces, there 

 must be a law determining both its time and mode of oper- 

 ation is sufficiently* obvious ; but in the mean time that law 

 lies altogether beyond the indications of science, and we 

 must content ourselves with mere descriptions of pheno- 

 mena and explanations of function. What the cause of 

 volcanic energy 1 what the periodicity of its discharges 1 

 what the times and directions of earthquake convulsions 1 

 and what the law which regulates the shifting of vulcan- 

 ism from centres that were once disturbed to newer areas ? 

 are questions to which science can give no satisfactory 

 answer, and generations may pass before even the way to a 

 solution is indicated. What we want is, first, a more minute 

 investigation of the products of volcanoes, that it may lead 

 to a knowledge of the decompositions taking place within 

 the earth's interior ; second, observations as to the connec- 

 tion between earthquake throes and volcanic discharges; 

 third, a record of the times and directions of earthquake 

 convulsions ; and, fourthly, an accurate series of tabulations 

 and maps to assist us in our deductions. All this is little 

 more than merely beginning to be done. Chemistry and 

 physics have only recently been directed to the subject; 

 and Seismology or Seismography (the science of earth-shocks) 



