xi CLEAVAGE i$j 



in different substances, even in so homqjenaout a body as 

 wax poured in a melted state upon a surface of glass. 

 Rocks in which the change has been superinduced are 

 aid to be </ror/, and the change itself is termed 



Considerable practice is required todUtinguish between 

 the fissile structure thus developed by cleavage, and that 

 due to original lamination of deposit Should the rock 

 consist of alternate bands of different textures or colours, 

 such alternation will of itself be sufficient to show the 

 bedding ; while a further test will be found in the frequent 



difference in the fineness of the cleavage as it passes from 

 one rock into another. Fine-grained argillaceous rocks 

 assume the most perfect cleavage ; hence their value as 

 slates. Their original bedding may be entirely effaced. 

 Sandy and gritty rocks do not allow of the development 

 of such fine divisional planes. Consequently the 

 cleavage-lines may actually be seen to stop when they 

 reach an arenaceous sr ig. 53) and begin again 



on the further side at the next argillaceous band. Where 

 no such intercalation of different strata can be observed, 

 the geologist looks for lines of colour corresponding with 

 original lamination. Should these fail, he may for an 

 interval find it impossible to make sure in what direction 

 the lines of stratification run. It will be perceived from 



