Sacked constables gathered round first of remote rock formations (8)
I believe the answer is:
outcrops
'rock formations' is the definition.
'sacked constables gathered round first of remote' is the wordplay.
'sacked' becomes 'out'.
'constables' becomes 'cops'.
'gathered round' means one lot of letters goes inside another.
'first of' says to take the initial letters.
The initial letter of 'remote' is 'r'.
'cops' placed around 'r' is 'crops'.
'out'+'crops'='OUTCROPS'
(Other definitions for outcrops that I've seen before include "Exposed rock formations" , "exposed rocky areas" .)