48 H. I. JENSEN. 



course with masses of boulders and rolling stones that now are 

 scattered over the Bolivian plain (as at Santa Cruz de la Sierre). 

 Then the Peruvian waters forced their way through the Matto 

 Grosso ranges, and the waters of the Beni joined those of the 

 Madeira, after a nighty leap at the Esperanza Falls. — (" Frem," 

 May 14th, 1899. 



(3) Earthquakes connected with volcanic eruptions. — 

 These depend on the same cause as volcanoes which will 

 presently be discussed. They are partly comprised in the 

 class just discussed. 



(4) Earthquakes resulting from other causes insufficient 

 in themselves to bring about disturbances, but frequently 

 important liberating forces. — Occasionally two or more of 

 these secondary causes acting simultaneously in a region 

 of great instability, may precipitate an earthquake. Such 

 events as perigee, equinoxes, cyclonic disturbances and the 

 attraction of the planets I would be inclined to consider 

 secondary causes. Under this heading we may also place 

 the earthquakes which are attributed (a) to the loading of 

 parts of the earth's crust by sedimentation or organic 

 growth; and those due to (b) unloading of portions by sub- 

 aerial denudation and erosion. The Charleston earthquake 

 of 1886 was probably in no small way connected with the 

 immense sedimentation and organic growth in the Mexican 

 Gulf and in the Atlantic to the south-east of the United 

 States of America. The Cutch earthquake of 1819, and 

 the Cachar earthquake of 1869, were probably due to a 

 similar cause. 



The extensive earth disturbances of the year 1811 in 

 Europe, the earthquakes of 1833, 1855 and 1887, the Herzo- 

 genrath shocks between 1874 and 1877 and the Rhineland 

 earthquake of 1846 were probably all connected with un- 

 loading by denudation, a process which must hasten secular 

 cooling. Hence such earthquakes should be most frequent 

 at sunspot minima. 



