Iron doesn't begin to support type of rock passage (8)
I believe the answer is:
progress
'passage' is the definition.
(thesaurus)
I don't understand the rest of the clue.
Can you help me to learn more?
(Other definitions for progress that I've seen before include "Advance - promotion" , "Advancement" , "Satisfactory development" , "Relating to verse" , "Course" .)