374 



THE PLAN OF THE EA.RTH AND ITS CAUSES. 



he called di aclases. The directions of the Greenland fiords is deter- 

 mined by a similar series of intersecting- diaclastic fractures. Bertrand 

 has shown that the movements in the Paris Basin, the North Sea, and 

 English Channel have followed a double set of orthogonal intersecting 

 lines. 



But that the fracture lines or lines of weakness in the earth's crust 

 should intersect more or less rectangularly is natural on any theory 



of their formation. And such coinci- 

 dences as those pointed out by Elie de 

 Beaumont in support of his system are 

 inevitable in so crumpled a globe as 

 ours, but they are not sufficiently nu- 

 merous to be convincing, especially in 

 face of the fundamental differences be- 

 tween the facts of geography and Elie 

 de Beaumont's elaborate artificial sys- 

 tem. His theory could only be applied 

 to a symmetrical world; 1 in a dodeca- 

 hedron the opposite faces are always 

 similar and parallel ; in Elie de Beau- 

 mont's network the antipodal areas are 

 always similar. But, as we have seen, 

 the fundamental fact in the plan of the 

 world is that opposite areas are dis- 

 similar. In crystallographic language, 

 the lithosphere is hemihedral, not holo- 

 hedral, and no scheme based on a holo- 

 hedral form will serve. It is the rec- 

 ognition of this principle that led to 

 the next great advance. 



Fig. 4. 

 RELATIONS OF A TETRAHEDRAL LITHOSPHERE 

 TO ITS HYDROSPHERE. FIG. 4a REPRESENTS 

 THE ARRANGEMENT IN A SIMPLE TETRAHE- 

 DRON. FIG. 4b ILLUSTRATES THE CASE OF 

 A MODIFIED TETRAHEDRON (SUCH AS SHOWN 

 IN FIG. 5b), BY A SECTION PASSING ON THE 

 LEFT THROUGH A TETRAHEDRAL COIGN, 

 AND ON THE RIGHT THROUGH THE OP- 

 POSITE TETRAHEDRAL FACE. THE SHADED 

 AREAS REPRESENT WATER. 



THE TETRAHEDRAL THEORY. 



Elie de Beaumont's scheme is now 

 mainly of historic interest, though Lef- 

 ort's recent map of the Nivernais shows 

 that it is still used as a workin g hypoth- 

 esis by some French geologists. But 

 Elie de Beaumont's theory marked an 

 epoch in this subject, for it led to the 



system of Mr. Lowthian Green, which far better meets the requirements 



of the case. 

 This system was founded in 1875, by Mr. Lowthian Green, in a work 



which was neglected or ridiculed at the time of its appearance. Like 



'This objection applies also to various later modifications of Elie de Beaumont's 

 principle, such as those of Owen, or to the more than local acceptance of the 

 diaclases of Daubrt'e or orthogonal cross folds of Bertrand. 



