I907.J AND MOUNTAIN FORMATION. 399 



derangements due to earthquakes. Many of the dislocations of the 

 strata now seen on land originated when they were beneath the sea, 

 and it would be a mistake to attribute any considerable part of these 

 movements to seasonal or meteorological influences. It may be that 

 the shape of the two sides of a valley undergoes an infinitesimal 

 deformation from these causes, yet no important effects depend on 

 such small deformations. They are all very superficial in character, 

 whereas the causes which have folded the rocks of the earth's crust 

 have been much more deep seated, and originate principally in earth- 

 quakes. When we see folded strata laid bare by erosion therefore 

 we may assign the greater part of such effects to the " gentle warp- 

 ing of the soil " experienced in the dreadful shakings and derange- 

 ments due to earthquakes of the world-shaking class. In observed 

 plications of the strata earthquakes have supplied the principal part 

 of the disturbing force. The important uplifts have all arisen in 

 this way, and the instability thus resulting has produced the smaller 

 displacements noted where the earth is settling. 



The ground is more or less flexible near the surface, and sensible 

 sagging may be produced by loading, but such effects are shallow 

 and small in amount, and it would be a mistake to attribute to this 

 cause important deformations of the strata. Is not such phrase- 

 ology as the " gentle warping of the soil " therefore very unfortunate 

 and misleading, and should it not be entirely given up? 



§ 1 8. Radium and other Atomic Sources of Energy. — In the 

 paper on the " Temperature of the Earth " we adhered to the gravita- 

 tional theory as the only one which could be subjected to strict 

 calculation. It is of course possible that there may exist in our 

 planet unknown sources of atomic or subatomic energy such as are 

 shown in radium and the related elements, which exhibit similar 

 radio-active properties. At present, however, the amount of these 

 elements known to exist in the earth is excessively small, and 

 although this might account for the earth's internal heat; yet as 

 gravitation is known to be a real cause and has been found sufficient 

 to explain the observed phenomena, it is natural that a known source 

 of energy which can be subjected to strict calculation should be pre- 

 ferred to one which is so wholly unknown. 



