154 COSMOS. 



mountain chains and of stratified mountain masses is con- 

 sidered in relation to its dependence upon the direction of 

 magnetic lines, more especially the isoclinal and isodynamic 

 systems. I am far from denying the influence of all cosmical 

 primary forces — dynamic and chemical forces — as well as of 

 magnetic and electrical currents on the formation of crystal- 

 line rocks and the filling up of veins;* but owing to the 

 progressive movement of all magnetic lines and their conse- 

 #quent change of form, their present position can teach us 

 nothing in reference to the* direction in primeval ages of 

 mountain chains, which have been upheaved at very differ- 

 ent epochs, or to the consolidation of the earth's crust, from 

 which heat was being radiated during the process of its 

 hardening. 



Of a different order, not referring generally to- terrestrial 

 magnetism, but merely to very partial local relations, are 

 those geognostic phenomena which have been designated by 

 the name of the magnetism! of mountain masses. These 

 phenomena engaged much of my attention before my Amer- 

 ican expedition, at a time when I was occupied in examin- 

 ing the magnetic serpentine rock of the Haidberg mountain, 

 in Franconia, in 1796, and then gave occasion in Germany 

 to a considerable amount of literary dissension, which, how- 

 ever, was of a very harmless nature. They present a num- 

 ber of problems, which are by no means incapable of solu- 

 tion, but which have been much neglected in recent times, 

 and only very imperfectly investigated both as regards ob- 

 servation and experiment. The force of this magnetism of 

 rocks may be tested for the determination of the increase of 

 magnetic intensity by means of pendulum experiments, and 

 by the deflection of the needle in broken-off fragments of 

 hornblende and chloritic schists, serpentine, syenite, dolerite, 

 basalt, melaphyre, and trachyte. We may in this manner 

 decide, by a comparison of the specific gravity, by the rins- 

 ing of finely pulverized masses, and by the application of the 

 microscope, whether the intensity of the polarity may not 

 depend in various ways upon the relative position, rather 

 than upon the quantity, of the granules of magnetic iron 



* Delesse, Sur rassociation des mineraux dans les roches qui ont 

 un pouvoir magnetique eleve, in the Comptes rendus de I'Acad. des Sc, 

 t. xxxi., 1850, p. 806 ; and Annales des Mines, 4eme Serie, t. xv. 

 (1849), p. 130. 



t Reich, Ueher Gebirgs-und Gesteins-Magnetismus, in Poggend., 

 Ann.y bd. Ixvii., s. 36. 



