43 



CHAPTER VII. 



ON THE ORDER OF THE SPLITS, FRACTURES AND DISLOCA- 

 TIONS IN THE PRIMARY ROCKS, INCLUDING THE SUPER- 

 INCUMBENT SEDIMENTARY MASSES. 



According to the meridional structure of the globe described 

 in the preceding chapters, the general appearance of the surface 

 may be compared to the grain of a fruit ; such for instance as 

 an orange or melon, having a grain from pole to pole. Indeed, 

 when we look at the moon through a telescope, and especially 

 in the clear atmosphere of the tropics, she also presents such an 

 appearance. We observe numerous luminous rays radiating from 

 the pole facing the south, which are seen diverging towards 

 her equator, some of which extend to the northern edge *. Pro- 

 bably the external part of all fruits, possessing two opposite poles, 

 is formed in the same manner as the crystalline shell of our 

 globe. 



This meridional action, producing the crystallization, fibrous 

 and laminated structure of the consolidated masses, must neces- 

 sarily cause a very considerable tensional strain. Let us, for 

 example, suppose a given area were undergoing elongation by 

 the polar force ; should any part of the mass not possess suffi- 

 cient tenacity to allow it to extend, fractures would ensue, and 

 those would take place more or less transversely to the direction 

 of the force ; the nature and number of these ruptures would 

 depend on the variable state of the mass. Should the rock con- 

 tain subordinate channels of unequal elasticity and variable width, 

 splits would occur longitudinally or diagonally to the grain, ac- 

 cording to the direction of the least resistance. That the rocks 

 are elastic and subject to undulating motions, capable of being 

 elongated, and not, as is too commonly supposed, a rigid incom- 

 pressible mass, is a fact which we need not further insist upon. 

 We have therefore the following series of lines as a necessary 



* The bright polar focus is considered a volcano by the Plutonists, and the ra- 

 diating rays streams of lava ; it requires no ordinary stretch of the imagination 

 to suppose such conditions without causing some awful catastrophes. 



