Geology and Magnetism. 521 



the masses (called heaves by the miners). These are the effects of 

 the horizontal or diagonal motion of the individual strips of rocks 

 between the splits from their original position. The great heaves 

 are produced by the northward action of the rocks between the 

 polar splits ; the slides observed in the east and west fractures are 

 few t and generally insignificant ; they are the effect of wedges of 

 rocks squeezed between great splits. 



These dislocations have created great discussions, and have 

 caused very opposite opinions, owing principally to the impossibility 

 of restoring the continuity of all the fractures on both sides of the 

 splits. A very little reflection must show that such an agreement 

 in all the fractures could not be expected. In the first place, the 

 ruptures across the splits would necessarily take place in the direc- 

 tion of the least resistance, be that in a direct line or not ; it does 

 not follow that it should be straight across the split. If, again, we 

 consider that the rocks are exposed to the continual action of the 

 polar current, and therefore subject to a slow movement northward, 

 there would necessarily be fractures taking place periodically in the 

 same masses, i. e. when the " heaves" are only 1, 10, 20, 30, 50 

 feet ; how then would it be possible to restore the continuity of the 

 whole series of fractures ? It is well known, and can be proved that 

 the fractures have occurred at different periods. It is like attempt- 

 ing to refit pieces of ice, after having been broken and subjected to 

 repeated movements and reunited again by repeated freezing, as 

 to try to restore dislocated masses of rocks in the primary base. 



When we consider the semifluid nature of the masses, and their 

 permitting a continual molecular action through their pores in the 

 meridian direction, like the current of sap in a living tree, we need 

 not be surprised that the wall of the fractures, cannot always be 

 refitted ; their ruptured sides are altered by the chemical action in 

 a very short time ; the southern parts of which are often seen pene- 

 trating into the northern by a new cleavage formed subsequently to 

 the filling of the cracks, as represented in Plate XL* 



Miners are well aware that the sides of veins often bulge out in 



defiance of all mechanical resistance : it requires a considerable 



practical knowledge to keep them open to extract the mineral, 



particularly in very wet ground. When the splits happen to be in 



* See Note, p. 518. 



