Following steamship covered in fuel - it's very old and rocky (6)
I believe the answer is:
fossil
'very old and rocky' is the definition.
(fossils are found in rocks)
'following steamship covered in fuel' is the wordplay.
'following' becomes 'f' (used when citing page numbers etc).
'steamship' becomes 'ss' (nautical abbreviation).
'covered in' means one lot of letters goes inside another.
'fuel' becomes 'oil' (oil is a type of fuel).
'ss' put into 'oil' is 'ossil'.
'f'+'ossil'='FOSSIL'
'it's' is the link.
(Other definitions for fossil that I've seen before include "This fuel is natural, extracted from the ground" , "Relic of bygone age" , "Antiquated person" , "Ancient remnant hardened in rock" , "Preserved trace of an ancient plant or animal" .)