134 ORIGIN AND DEVELOPMENT OF ORE DEPOSITS. 



The "mountain system" theories of M. Elie de Beaumont* 

 are twofold. The first portion treats of the relative ages of 

 mountain chains, and to their grouping into contemporary and 

 parallel " elements." The second correlates the observed direc- 

 tions of the different systems according to an assumed geometric 

 law, by means of a "pentagonal network." We can accept the 

 first portion without of necessity adopting the second. 



M. Elie de Beaumont, in 1869, after correlating the recorded 

 observations of geologists in all parts of the world, announced 

 that he had been able to define 85 distinct mountain systems, 

 which included most of the principal bands of contortion and 

 axes of upheaval on the earth's surface. He referred each 

 system to some properly defined great circle, all the parallel 

 contortions within 10° on either side being regarded as belonging 

 to the system. He observes that any particular mountain-chain 

 may belong to one system, or may be made up of "links" 

 belonging to two or more systems of different dates. The 

 relative ages of these systems can be determined by observing 

 the ages of the stratified rocks which are respectively elevated 

 and undisturbed on their flanks. 



M. Leon Moissenet finds that eleven of the more ancient of 

 Beaumont's systems of fracture are represented in various parts 

 of Cornwall and "West Devon, six running east and west, and 

 five north and south. Connected with these eleven "systems," 

 he detects 132 distinct bearings of lode-fissures, as under : — 



a. The eleven systems 11 bearings. 



b. Their perpendiculars 11 ,, 



c. The bisectrices of the acute angles 



formed by pairs of adjoining 

 systemsf 55 ,, 



d. The perpendiculars of these bisec- 



trices 55 ,, 



Total 132 



^Notice sur les systemes de Montagues, Paris, 1852. See also Observations 

 on the Lodes of Cornwall, by M. Leon Moissenet, translated by J. H. Collins, 

 Truro, 1877. 



fThe groups c and d require a word of explanation. Lode fissures are rarely 

 straight, those which are best developed seem to be made up of distinct " systems 



