256 SEE— FURTHER RESEARCHES ON [April 24, 



The earth is not shrinking and the crust does not tend to sepa- 

 rate itself from the underlayers, except where the lava has been 

 expelled from beneath it by earthquakes. The collapse of the crust 

 when thus undermined, however, shows that it wall not support its 

 own weight even for a short distance. Over such small areas the 

 crust may be taken as part of a plane, or sometimes as concave, 

 where subsidence is already at work, and hence the theory of the 

 arch or dome is scarcely applicable ; yet the observed collapse and 

 sinking, even where the area is no larger than in ocean troughs, 

 confirms the above conclusions regarding the total inability of the 

 crust to support itself. 



Could therefore anything be more absurd than to discuss the 

 stresses in the crust due to the progress of secular cooling? Stresses 

 arise only where mountain making is in progress, and therefore 

 chiefly near the oceans, but never appear far inland ; and are wholly 

 due to the pressure arising from steam-saturated rock and the expul- 

 sion of lava from beneath the oceans, or to movements traceable to 

 surface water slowly sinking into the earth. The theory of arches 

 and domes therefore confirms the present theory, but this result is 

 indirect ; and such lines of thought did not enable geologists and 

 physicists to reach correct conceptions regarding the physics of the 

 earth's crust. 



§ 50. 0)1 the Doctrine that Earthquake Movements depend on 

 Slight Ineqtialities of Loading, and on the Abandoned Theory that 

 the Earth is a Failing Structure. — As the crust of the earth is made 

 up of solid rock and soil arising from the disintegration of rock of 

 various kinds, and as this material is elastic and yields under pres- 

 sure, it naturally occurred to physicists that inequalities of surface 

 loading deposited on adjacent areas would impose upon the under- 

 lying crust unequal stresses, and perhaps give rise to relative move- 

 ments. Thus many physicists, in default of a better theory, have 

 supposed that surface loads, depending on erosion and sedimenta- 

 tion, tides and varying barometric pressure, would be adequate to 

 produce stresses that would cause readjustment of the surface strata 

 and perhaps movements of faults in earthquakes. 



It is undeniable that these varying loads do produce some small 

 effects, and very slight changes of level mav often arise in this 



