SUNSPOTS AND VOLCANIC AND SEISMIC PHENOMENA. 47 



solar phenomena react so rapidly on the magmas of the 

 earth, and the rise of isogeotherms so slowly. 



For the purposes of this paper I propose now to classify 

 earthquakes in accordance with the causes producing them. 



(1) Earthquakes caused by the cooling, hence contrac- 

 tion of the contracting zone of the earth's crust. — These 

 should be of greatest violence and frequency when the 

 earth radiates most heat, or other energy, into space, that 

 is, at sunspot minima. The great majority of earthquakes 

 and earthquake shocks undoubtedly fall in this group. 



(2) Earthquakes which arise from the heating of strata. 

 Tangential strain and shearing, especially where beds 

 which are suffering a rise of isogeotherms (and consequently 

 expansion and folding) abut on strata undergoing contrac- 

 tion must result in faulting. In parts of Japan, in Java, 

 in parts of the Peruvian and Bolivian Andes, which are 

 regions undergoing elevation from isogeothermal rise, 

 earthquakes of this type are frequent ; and in such localities 

 no true earthquake periodicity can be expected. The 

 increase of solar heat during sunspot maxima may acceler- 

 ate the folding of sedimentary strata by screening the earth 

 from radiation into space. This would result in earthquake 

 shocks. At times of sunspot minima the increased shrink- 

 age of adjoining rock masses would also result in fractures 

 along the lines of weakness of the earth's crust, and the 

 junction of old rocks with recently upheaved and expanding 

 sediments is usually a line of weakness. 



The Mendoza earthquake of 1861 was probably the result 

 of rise of isogeotherms in the recently upheaved sediments 

 of the La Plata region. 



In the Argentine region sediments were deposited when the 

 Amazon was yet an insignificant stream, and the La Plata drained 

 the Peruvian area. Later on the latter river blocked its southern 



