owing to the want of a better acquaintance with the geological 

 nature of rocks ; yet no definite rules have ever been suggested 

 to avoid the repetition of such errors. It has been triumphantly 

 appealed to, as one important generalization among others esta- 

 blished by geology for the aid of miners, that the proximity of 

 pyrogenous and sedimentary rocks, and the changes thus super- 

 induced upon the latter regulate the enrichment and product- 

 iveness of mineral veins. In this manner, it is said, that cer- 

 tainty and precision have been given to a knowledge which was 

 before only vague and partial. It is not easy to comprehend 

 the meaning, much less the application, of the above principle 

 to mining, or any other works in rocks. There is scarcely a 

 geological section furnished of the primary series in which the 

 lamina? of the crystalline slates are not coafounded with the 

 planes of the sedimentary strata; and also exhibiting veins with 

 an overflow of melted matter, &c, showing volcanic effects, to 

 explain phenomena with which they have no connexion. Every 

 hornblendic vein is now called ancient lava ; and igneous or vol- 

 canic rocks are terms of common occurrence. We shall en- 

 deavour to show that there is no foundation for assuming such 

 an igneous element, and that the crystalline rocks and the veins 

 are formed by polar forces according to geometrical laws, as 

 uniform as any other physical phenomena of the material world. 



This brief outline of the science is not brought forward with 

 the view of showing the inconsistencies of the existing hypo- 

 theses to explain the facts, nor to gratify idle curiosity by enter- 

 ing into pure speculative questions, but to point out a general 

 law, which is simple and practically useful, consistent with the 

 general law of terrestrial physics, and which has been suc- 

 cessfully applied for several years in mining and other geological 

 operations. 



Although the subject is confined here within narrow limits, 

 and must necessarily be very imperfectly described, yet it is 

 hoped that, by the aid of the accompanying illustrations, the 

 general bearing of the magnetical theory will be comprehended, 

 and found to rest on unquestionable data, without straining any 

 facts, but simply following the legitimate consequences arising 

 from cause and effect, proved by direct examination and experi- 

 ment. 



