i 



XllT 



Ul 



a 



fti 



e 



t^r 



-♦H^ 



) 



' an 

 'Tie 



fthe 



U 



) 



at 



L 



itlie 



* 



the 

 I the 



tions 



mces 



I 



the 



need 



IT ID 



iistly 



5 jet 

 ,to 



lieDi 



boiit 





tii^ 



Ch. XXXIII.] FLEXIBILITY OF THE EAETH'S CEUST. 



229 



moon is in perigee^ or nearest the earthy than at other periods, 

 when that satellite being less near is exerting a minor degree 

 offeree, or less strain npon the solid crust of our planet. In 

 like manner he thinks he has detected a relation between the 

 frequency of earthquakes and our winter and summer solstices, 

 the greatest number of shocks occurring in perihelion when 

 the sun is nearest, and the least number in aphelion wdien 

 it is farthest from the earth."^ On this subject Sir John 

 Herschel remarks, ' The action of the sun and moon, though 

 it cannot produce a tide in the solid crust of the earth, tends 

 to do so, and were it fluid would produce it. It does there- 

 fore, in point of fact, bring the solid portions of the earth's 

 surface into a state alternately of strain and compression.' t 

 Sir John Herschel, when endeavouring to suggest a cause 

 for the frequent proximity of chains of active volcanos, like 

 the Andes, to the sea, assumes that the solid bottom of the 

 latter and the neighbouring land may be regarded as float- 

 ing on a subterranean fluid mass. The land, he observes, is 



always undergoing w^aste by aqueous action, and portions of 



its solid matter are carried down in tlie form of sediment into 



the sea. Bj this means 



ocean is pressed 



down, while the continent is relieved of ]3ressiire, and this 

 brings about a state of strain in the crust which will crack 

 in its weakest part, the heavy side going down, and the light 



side rising. 



out through the rent. 



t 



•ranean fiery matter will then burst 

 as water oozes up when a crack 



of 



me 



very partial application, for active volcanos, even such as 

 are on the borders of continents, are rarely situated where 

 great deltas have been forming, whether in pliocene or post- 

 tertiary times. The number, also, of active volcanos in 

 oceanic islands is very great, not only in the Pacific, but 

 equally in the Atlantic, where no load of coral matter or any 

 sedimentary deposits derived from the waste of neighbouring 

 lands can cause a partial weighting and pressing down of 

 a supposed flexible crust. 



* Alexis Perrey, Propositions sur les Scientific Subjects, 1866, p. 45. 

 TremLlements de Terra, 1863. | Herschel, ibid. p. 12. 



T -Herscliel, Familiar Lectures on 



