652 



WM. HERBERT HOBBS 



perhaps, likewise be best explained through a change, and here a 

 reduction in width, of individual joint spaces. To this change may 

 be added the effect of some actual compression of the unfractured 



J\. 



Fig. 7. — Diagram to illustrate the narrowing of valleys during earthquakes as a 

 result of crustal contraction, {A) before contraction; (B) after contraction. 



portions of the shell. In Fig. 7 let A represent in its lower portion a 

 section of the outermost consolidated shell of the lithosphere, and in 

 its upper portion the mantle of unconsolidated deposits in which the 



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Fig. 8. — Diagram to illustrate the pushing up of the beds of rivers during earth- 

 quakes as a consequence of crustal contraction, (A) before contraction; {B) after 

 contraction. 



valleys have been cut. As the compression of the shell reduces the 

 width of the joint spaces and otherwise diminishes the superficies 

 of the shell, its envelop of loose material by reason of its lack of 



