The History of Things 57 



shell of materials bordering upon fusion," which 

 Sir John Murray calls the "tektosphere." On 

 this plastic shell there rests the heterogeneous and 

 wrinkled crust or lithosphere, always slightly- 

 pulsating. 



Then followed what may be called the wrinkling 

 and folding of the earth's crust. If the solid core 

 slowly contracted, the primitive crust in accommo- 

 dating itself through changes in the plastic shell 

 or tektosphere to the shrinkage within, would be 

 buckled, warped, and thrown into ridges. "The 

 contraction of the interior of the earth, consequent 

 on its loss of heat, causes the crust to fall upon it 

 in folds, which rise over the continents and sink 

 under the oceans, and the flexure of the area of 

 sedimentation is partly a consequence of this fold- 

 ing, partly of overloading." 1 The continents may 

 be due to contractions of the whole crust, while 

 mountains may be due to foldings of the outer 

 layers through tangential stress brought about by 

 contractions of the deepest layers. 2 Here we have 

 to do with local collapses or dislocations of the 

 crust and there with great lateral thrusts. As in 

 pack ice, there may have been unyielding masses, 

 which had to be piled one upon the other, while 

 other masses may have been simply overlapped. 



1 Sollas, loc. cit. 



2 See the epoch-making work of Suess: " Der Antlitz der 

 Erde" (1897). 



