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diate. This radiation is sometimes so disposed 

 that the strata diverge from the upper visible edge 

 of the vertical stratum ; while, at others, they con- 

 verge to ware's it. 



; In some instances of the latter disposition it 

 can only be known that two strata meet in an angle 

 like the roof of a house ; the intermediate rock 

 being inaccessible. 



Such reversals of the dip are sometimes re- 

 peated several times in the horizontal space occu- 

 pied by one set of strata. 



One set of strata is sometimes found occupying 

 a limited space, and lying on another stratum, or 

 set of strata, in such a manner as to present a con- 

 siderable depth in the central parts and to dimi- 

 nish gradually towards the edge. Such a collec- 

 tion has been called a basin ; and, under favour- 

 able circumstances, each stratum of it will in some 

 place be found in contact with the inferior rock on 

 which the whole reposes. 



: The thickness, or depth, if in a position ap- 

 proaching to the horizontal, of any series of strata, 

 is extremely various, even from a few yards up- 



