

174 



GEOLOG!f. 



[Sect. VI 



would probably give striking results. The range or strike 



of the cleavage is uniform over surprisingly large areas ; 

 whereas botli the angle and point of dip varies much • 

 but there is reason to believe that the planes of inclination, 

 examined across a wide tract transversely to the ranoe, will 



fall into order and show that thev are the truncat^-d edo-es 

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a tew great curves or domes. The relation of the 

 •leavage-planes to those of the stratification, or axes of 

 elevation, should be carefully noted, and likewise to the 

 general outline of the whole country. Long sections at 

 right angles to the strike of the cleavage, with the dip 

 oarefully protracted on paper, would be highly interest- 

 ing. When two chains of hills, each having its inde- 

 pendent cleavage, cross each other, careful observation., 

 should be made. In all cases, any mineralogical differ- 



ence 



however slight, in the parallel cleavage-layers, 

 deserves attention ; but observations on this head would 

 be hardly trustworthy, without the planes of stratification 

 were so distinct that there could be no possibility of con- 

 founding (as has often happened) cleavage and stratifica- 

 tion. Where a stratum of sandstone, or of any other 

 rock without cleavage, is interstratified with a slaty rock 

 the siu-fece of junction ought to be minutely examined, to 

 see if the slate has slipped along the planes of cleavage 

 ..r whether again the mass has not been either stretched 



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or compressed at right angles to these same planes. 



Fossil shells hav^e been 



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rocks, wliich have had their shapes greatly a'^ered, and 

 all in the same direction ; here then we have a guide to 

 judge of the amount and direction of the mechanical 



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