34 Matured /HMracles, 



a re-arrangement of the particles of which the 

 slate is made up has taken place, so that their 

 longest dimensions now are in a direction that 

 crosses the stratifications as originally laid 

 down. 



The effect of this is twofold. First, the 

 material is compressed into a denser, closer 

 form, and then, the lines of cleavage are 

 changed, or to express it in more common lan- 

 guage, the grain has been changed. So that 

 when it splits up it runs crosswise of the 

 original layers as the water deposited them, 

 and this produces the different shadings so 

 often seen in different slate. Shale splits in 

 line with its layers; slate splits across that 

 line. 



Let us go back a moment to our experiment 

 with the lump of clay. If we examined the 

 mixture before submitted to pressure we 

 should find that the oblong particles of which 

 it was made up would stand in all directions, 

 hit or miss, and if we should dry this lump of 

 clay it would have no special lines of cleavage. 

 But the moment we have submitted it to a 

 certain amount of pressure we find that lines 

 of cleavage have been established, and that the 

 particles have been rearranged so that their 

 longest dimensions are all in one direction, 

 which coincides with the cleavage lines. If 

 we should now take this same piece of clay 

 and subject it to a pressure at right angles to 



