CHAP. 6.] INTRUSIVE TRAPS. 65 



aqueous strata : sometimes portions of the latter are completety en- 

 veloped in the trap as already mentioned, or the latter has found its 

 way in such quantity between the beds that considerable hills com- 

 posed of it may be seen supporting caps of white silicious altered 

 sandstone. 



Other places occur where intrusions are so numerous, and so frequently 

 intercalated with the beds, that appearances of the traps being contem- 

 poraneous are often presented in detail, alternations of the aqueous and 

 igneous rocks taking place every few yards, and the aspect of the ground 

 being indescribably confused. 



The changes produced in the containing rocks by contact with the 



traps are sometimes extreme, whole beds some- 

 Alterations, 



times appearing to have been altered in sii?i into 



rock having much more the splintery nature, dark color, and general 



aspect of the trap than that of their adjacent unaltered portions. 



In most cases the difference of texture between the aqueous and 

 Igneous rocks has produced differences in the form of the ground ; the 

 latter standing out as hills, frequently conical or forming the summits 

 of cones, parts of which are composed of the other rocks. 



Dykes are numerous in some localities, but follow no definite 

 arrangement as to direction, more frequently 



DvlcGS. 



crossing the beds than following their strike. No 

 dykes are known in the purely aqueous tertiary rocks of Kuteh, 

 but some doubtful cases of dykes of purple trap occur in the sub- 

 nummulitic group. 



( 65 ) 



