Lead batteries found in crumbly soil consisting of clay and lime on the ultimate hard rock (6)
I believe the answer is:
marble
'hard rock' is the definition.
(I've seen this before)
'lead batteries found in crumbly soil' is the wordplay.
'lead' indicates taking the first letters (I've seen 'leading' mean this).
'found in' means one lot of letters goes inside another.
'crumbly soil' becomes 'marle' (I can't explain this - if you can you should give a lot more credence to this answer).
The first letter of 'batteries' is 'b'.
'b' placed within 'marle' is 'MARBLE'.
'consisting of clay and lime on the ultimate' acts as a link.
This may not be right. Some or all of it may belong to another bit of the clue.
Can you help me to learn more?
(Other definitions for marble that I've seen before include "Crystalline limestone often used by sculptors" , "Rock used for building and sculpture" , "Ornamental stone" , "Polished rock used in sculpture" , "Small ball of glass used in games" .)