x9o8.] THE PHYSICS OF THE EARTH. 255 



of the earth's crust were Hfted vertically b}' the pushing of lava 

 beneath them. It is in this way that all such walls of granite and 

 other towering rock are to be explained, and the fact that the sea 

 still encroaches on them shows how the movements came about. 

 Probably there has been little vertical movement for a long time 

 along the coast of Norway, and subsidence as well as elevation may 

 have taken place, both here and elsewhere. Subsidence is common 

 along most sea coasts, but it does not prevail in the long run, as 

 is proved by Professor Suess's work, showing a universal lowering 

 of the strand line throughout the world. 



§ 49. The Theory of Arehes and Domes Inapplicable to the Crust 

 of the Earth, because the Globe is not Shrinking hut actually Ex- 

 panding.— In Chamberlin and Salisbury's " Geology," Vol. I, p. 583, 

 we find the statement that 



" The principle of the dome is brought into pla}' whenever an interior shell 

 shrinks away, or tends to shrink awa}-, from an outer one which does not 

 shrink. In this case there is a free outer surface and a more or less un- 

 supported under surface towards which motion is possible. The dome may, 

 therefore, yield by crushing or by contortion." 



Owing to the important part the domed form of the crust has played 



in theories of deformation, these authors give quantitive results 



calculated by Hoskins, showing that such a dome of continental 



dimensions, if unsupported froiu below, would sustain only i/§2jth 



of its own zveight. 



In his consideration of the " Mathematical Theories of the 

 Earth" (Proe. Am. Assoc, for Adv. Sci., 1889, p. 49), Professor 

 R. S. Woodward reached the analogous conclusion that "If the 

 crust of the earth were self-supporting, its crushing strength would 

 have to be about thirty times that of the best cast steel, or five hun- 

 dred to one thousand times that of granite." 



In view of these results it is remarkable that any one should 

 have viewed the earth's crust as a wholly or partially self-support- 

 ing dome ; for it could not be supported even over a very small 

 area. And moreover secular cooling is wholly inadequate to cause 

 a separation of the interior layers from the crust. All that has been 

 published on this point, therefore, is inapplicable to the earth, be- 

 cause it rests on a false hypothesis. The supposed conditions have 

 no reality. 



