XII 



The Crust of the Earth 



233 



B 



theory of great ingenuity. Observing that all mountains of 

 elevation are of comparatively recent formation and are 

 ridged up out of thick sheets of sedimentary rock, he sup- 

 poses that the accumulation of sediment produces the 

 mountains. He points out 

 that if a large and deep 

 hollow in the Earth's crust 

 is rilled up with sediment 

 to the line AB (Fig. 48) at 

 the ordinary surface tem- 

 perature, say 60. the mass 

 now forming part of the 



FIG. 48. Mellard Reade's Theory _ of 

 Mountain Building. Light shading 

 shows original crust of the Earth, 

 dark shading sediment ; dark lines 

 original isotherms, fine lines isotherms 

 after deposition of sediment. 



Earth's crust will grow 

 warmer until, if the surface 

 temperature remains at 60, 

 that at the depth of 1200 feet at 80, and so on (dark lines in 

 figure), the covering in of the cavity raises the tempera- 

 ture throughout by preventing the loss of heat through 

 the crust, the new positions of the temperatures of 60 and 

 80 being shown by fine lines in figure. The warmed up 

 strata necessarily expand, and as they cannot expand side- 

 ways or downward on account of the solid walls of the depres- 

 sion, they must expand upward, and the surface of the sheet 

 of sediment is thrown into a series of ridges, true synclines 

 and anticlines, like the surface of a cake as it rises in being 

 baked. In Jhis theory also the energy which does the 

 work of elevating the mountain range is derived from the 

 interior of the Earth. 



REFERENCES 



1 J. Prestwich, " On Underground Temperature," Proc. Roy. 

 Soc. xli. (1886). 



2 The Eruption of Krakatoa, edited by G. J. Symons. Triibner 

 and Co., 1888. 



3 "Model of an Earthquake," Nature, xxxvii. 297 (1888). 



4 H. M. Cadell, " Experimental Researches on Mountain Build- 

 ing," Tr&ns. Roy. Soc. Ed. xxxv. 337 (1888) ; or Nature^ xxxvii. 

 488. 



BOOKS OF REFERENCE 



See end of Chapter XIV. 



