DYNAMICAL GEOLOGY. 301 



According to Elie de Beaumont, the ages of the mountain- 

 systems as a rule correspond with the limits of geological 

 formations, and therefore also with the "revolutions" indi- 

 cated by Cuvier in the development of organic creation. The 

 mountain-systems might in his opinion be regarded as chrono- 

 logical documents bearing witness to the paroxysmal stages in 

 the physical history of the earth's crust. He then attempted 

 to ascertain after this method the ages of the various 

 mountain-systems in Europe, deriving his facts partly from 

 his own observations, partly from literature. 



While engaged on this inquiry, Elie de Beaumont became 

 greatly impressed with the parallelism of the strike in the 

 several component elements of a mountain-system. He 

 remembered a saying of Werner's, that mineral veins with 

 parallel strike afford evidence of the simultaneous origin of 

 the vein fissures, and he applied this principle to mountain- 

 systems, endeavouring to prove in the most detailed manner 

 that mountain-systems or ranges with parallel strike were of 

 simultaneous origin. The spherical form of the earth made it, 

 however, difficult to determine the parallelism of mountain- 

 systems far remote from one another, since in such cases the 

 same term of geographical orientation would be used to 

 describe directions which were not by any means parallel. 

 Elie de Beaumont met this difficulty by treating the mountain- 

 systems as tangents of earth-circles and arguing from the 

 parallelism of the tangents. He regarded as parallel all 

 mountain-systems which crossed the meridian at a like angle. 



With the principle of parallelism, Elie de Beaumont left 

 the sure ground of inductive reasoning and entered into 

 speculative matter, which unfortunately he continued to discuss 

 during the remainder of his life. In his description of the 

 mountains of Europe, published in 1852, they are represented 

 as tangents of twenty-one circles, and from the inclination of 

 these circles to one another Elie de Beaumont deduced a 

 general geometrical law of orientation for the mountains of the 

 earth. He also constructed a "pentagonal net-work" of the 

 fifteen largest circles which corresponded to the corners of a 

 regular isogon in the centre of the earth, and made it the 

 fundamental basis of his elaborate scheme of the earth's 

 mountain-systems. But the famous " Reseau pentagonal " never 

 received general recognition, although it was much discussed 

 for a time by the personal adherents of Elie de Beaumont. 





