OVERLYING ROCKS. 491 



bite, epidote, and calcareous spar, occur as con- 

 stituent parts of the trap rocks ; most commonly, 

 they must be considered as accidental and foreign 

 ingredients, occurring in the amygdaloids, or 

 supra-compounded varieties. 



The various minerals that appertain to the 

 supra-compounded division of these rocks, and 

 those which occur in other modes imbedded in 

 them, will be enumerated in the Synopsis, and 

 require no particular notice here ; they must be 

 considered as accidental substances in their na- 

 tural repositories, and they produce in the former 

 case, a subdivision of varieties subsidiary to those 

 which arise from the different characters of the 

 the base in which they exist. The bases them- 

 selves vary, in these cases, as they do in the 

 simpler ones formerly enumerated ; although 

 wacke, and the claystones, under different degrees 

 of induration, are by far the most common. 



Such is a general sketch of the nature of the 

 trap rocks as far as my observations have per- 

 mitted me to delineate it, and on this foundation 

 is constructed the synoptical table that follows. 

 It is confessedly imperfect, but it will have per- 



