Exploit course in rock formation (9)
I believe the answer is:
anticline
'rock formation' is the definition.
(type of rock formation)
'exploit course' is the wordplay.
'exploit' becomes 'antic' (antics are exploits or escapades).
'course' becomes 'line' (synonyms).
'antic'+'line'='ANTICLINE'
'in' is the link.
(Other definitions for anticline that I've seen before include "Rocky ridge" , "fold" .)