1846.] SHARPE ON SLATY CLEAVAGE. 1 05 



either separately or in combination, for the immediate cause of slaty- 

 cleavage. I leave others to decide between them, contenting myself 

 with having supplied some of the materials upon which the decision 

 may be built. 



Much remains to be done before the subject can be exhausted, and 

 the direction of the cleavage planes must be examined over many 

 districts before the explanations here proposed can be received as 

 general laws. All that important branch of the subject which is con- 

 nected with crystallization has been left untouched, and since Mr. 

 Darwin has shown a connection between the cleavage of slate and 

 the foliation and apparent stratification of gneiss and other rocks of 

 similar character*, this alone will require long study in different 

 districts. These inquiries and others to which they may lead, may 

 guide us to conclusions very different from those which we might be 

 disposed to adopt in the present state of our knowledge. 



* Geological Observations on South America, chapter 6. 

 qmoa arii oi i 



.?. yd he': 



■fid-rr mini ft dil 

 -?Bxi xriair 



nh £>dt iBib 



oiojsdosni Ho iwbBimf 



