Geology and Magnetism. 519 



rock. It is found in the Brazils, Chili and New Granada, in the 

 tender part of porphyry and clay-slate. It is the destruction or 

 waste of these friable rocks that produces the rich alluvial soil of 

 America. 



The porphyry of Cornwall contains nests of yellow copper ore, 

 varying from a few ounces to several tons' weight. In North Wales 

 and Cumberland similar metalliferous rocks are common ; they are 

 also very abundant in Ireland. 



Moss copper is well known to miners ; it is the produce of a me- 

 talliferous rock, out of which it vegetates like common moss. Gold, 

 silver, pyrites, lead, and indeed all metals, may be seen occasionally 

 growing out of rocks where the situation and circumstances are 

 favourable for their formation. 



The minerals are found in the rocks in solution as common as 

 in the solid, indeed it is the state in which we consider them to be 

 previous to their crystallization. All rocks are more or less im- 

 pregnated with mineral solvents. The cupreous springs are very 

 abundant in Chili, Peru, New Granada, Cuba and New Brunswick : 

 they are to be seen also in Ireland, Anglesea, Spain and Hungary. 

 The copper in solution is obtained by precipitating it by means 

 of iron. The bog-iron ore is of similar origin, and is formed pre- 

 cisely in the same manner as the calcareous and siliceous tuffa." 



According to Mr. Hopkins, there are two great series of 

 splits and fractures in primary rocks, the one extending 

 in a meridional direction from pole, to pole, more or less 

 interrupted, and depending on the polar forces. The other 

 series extend from east to west, and are occasioned by the 

 contraction of the rocks in the direction of the grain. It is 

 to these last, that the peculiar rents and dislocations called 

 faults, are referred. 



" We have already shown that the polar grain is universally ob- 

 served ; the east and west fractures intersecting this structure are 

 seen in the Brazils and Chili, forming immense veins of quartz. In 

 Peru and Quito they are very abundant. In New Granada, on the 

 western Cordillera, which is principally formed of porphyritic 

 granite, the east and west fractures are very numerous, and are 



