262 DIRECTIVE FORCES. 



than that it is probable many of the structural con- 

 ditions of our planet are due to polarity. 



Mountain ranges observe a singular uniformity of 

 direction, and the cleavage planes of rock are evidently 

 determined by some all-pervading power. Mineral 

 bodies are not distributed in all rocks indiscriminately. 

 The primary formations hold one class of metalliferous 

 ores,, and the more recent ones another. This is not 

 to be regarded as in any way connected with their 

 respective ages, but with some peculiar condition of 

 the stone itself. The granite and slate rocks, at their 

 junctions, present the required conditions for the de- 

 posit of copper ore, while we find the limestones have 

 the characteristic physical state for accumulating lead 

 ore. Again, on examining any mineral vein, it will be 

 at once apparent that every particle of ore, and every crys- 

 tal of quartz or limestone, is disposed in a direction which 

 indicates the exercise of some powerful directive agency.* 



It appears, from all the results hitherto obtained, that 

 the magnetic and diamagnetic condition of bodies is 

 equally due to some peculiar property of matter in re- 

 lation to the other forms of electricity. We have not 

 yet arrived at the connecting link, but it does not appear 

 to be far distant. 



We have already referred to the statement made by 

 talented experimentalists, that magnetism has a powerful 

 influence in either retarding or accelerating chemical 

 combination. Beyond a doubt chemical action weakens 

 the power of a magnet ; but the disturbance which it 

 occasions in soft iron, on the contrary, appears to tend 

 to its receiving magnetism more readily, and retaining 

 it more permanently. Further investigations are, how- 



* In a work published by Mr. Evan Hopkins, entitled On the 

 Connexion of Geology with Terrestrial Magnetism, will be found 

 many valuable practical observations, made in this country and 

 the gold and silver districts of America ; Ivit the views taken by 

 the author are open to many objections. 



