EARTHQUAKES. 



Ill 



if long enough, would 

 rise to the same phe- 



It is evident, however, that Bunsen's theory of geyser-eruption is 

 independent of his theory of geyser-formation. A tube or fissure of 

 any kind, and formed in any 

 way, 

 give 



nomena. The Yellowstone 

 geysers have mounds or chim- 

 ney-like cones, but it is by 

 no means certain that the 

 whole length of their eruptive 

 tubes has been built up by 

 siliceous deposit. Bunsen's the- 

 ory of eruption none the less, 

 however, applies to these also. 



Fig. 95. 



-Ideal Section of a Geyser-Tube, according to 

 Bunsen. 



Section 3. — Earthquakes. 



Only very recently, and mainly through the labors of Mr. Mallet,* of 

 England, our knowledge on the subject of earthquakes has commenced 

 to take on scientific form. This slowness of advance has arisen not 

 from any want of materials, but from the great complexity of the phe- 

 nomena, their origin deep within the bowels of the earth and there- 

 fore removed from observation, and, more than all, from the surprise 

 and alarm usually produced unfitting the mind for scientific observa- 

 tion. For these reasons, until twenty or thirty years ago, the state of 

 knowledge on this subject was much the same as it was 2,000 years ago. 

 And yet now, we think, our knowledge of earthquakes is even more 

 advanced than that of volcanoes. 



Frequency. — Mallet, in his earthquake catalogue, has collected the 

 records of 6,830 earthquakes as occurring in 3,456 years previous to 

 1850 ; but, of that number, 3,240, or nearly one half, occurred in the 

 last fifty years ; not because earthquakes were more numerous, but be- 

 cause the records were more perfect. According to the more complete ' 

 catalogue of Alexis Perrey,f from 1843 to 1872, inclusive, there were 

 17,249, or 575 per annum. In Japan alone there are, on an average, two 

 shocks per day.]; It seems probable, therefore, that, considering the 

 fact that even now the larger number of earthquakes are not recorded, 

 occurring in mid-ocean or in uncivilized regions, the earth is constantly 

 quaking in some portion of its surface. 



Connection with other Forms of Igneous Agency. — The close connec- 

 tion of earthquakes with volcanoes is undoubted : 1. Volcanic eruptions, 



* Transactions of British Association, 1850-1858 ; also, Principles of Seismology, 

 f American Journal of Science, vol. xi, p. 233, 1876. 



\ Transactions of the Seismological Society of Japan, vol. vi, Part II, p. 79. Nature, 

 vol. xl, p. 657, 1889. 



