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its further application in directing him how to make new dis- 

 coveries renders it of inestimable value. It not only shows the 

 rocks in which mineral wealth is most likely to be contained, 

 but also those particular portions of them where the greatest 

 degree of remuneration may be expected. By this principle the 

 great laws which regulate the distribution of mineral veins, and 

 the arrangement of their subterranean treasures, are established. 

 The apparent and real " heaves " may be distinguished, and all 

 description of displacement can be ascertained on the same 

 mechanical principles. 



When the existence of subterranean electric currents was first 

 discovered by Mr. Fox in Cornwall, it was naturally anticipated 

 that they would afford some useful indications as to the relative 

 quantities of ore in different veins, and also as to the directions 

 in which they would be most productive. But on applying the 

 necessary apparatus, we find it very uncertain in its indications ; 

 local action is often produced so as to cause the currents to move 

 in all directions ; hence, although the principle is unquestion- 

 able, the mode of applying it to useful purposes is very defective. 

 Since we know that magnetic currents are the same, and go- 

 verned by the same identical power, all difficulties in the appli- 

 cation are removed, and the needle will always indicate the 

 true direction, free from the effects of local chemical action, and 

 in places where no mineral is visible. Indeed the knowledge of 

 the effects, in a limited and local form, is often perfectly and 

 accurately known to many, but more especially to the intelli- 

 gent mining captains of Cornwall, whose extensive experience 

 has naturally led them to an acquaintance with the nature and 

 distribution of the great mineral masses in that county. To 

 give consistency to the scattered elements thus acquired, to 

 show the mode in which they are connected, has been the main 

 object of this outline, and it is hoped that mining will be be- 

 nefited by it. It will show that parallelism of bunches depends 

 on the angular position of the lodes, and that it is an effect 

 arising from a primary cause. The miner complains that the 

 rapid progress of geology, and the geological surveys by eminent 

 geologists, have thrown no light on their operations, and that 

 hitherto geology is more indebted to mining than mining to 

 geology. However, such is not the case with magnetism; its 



