Geology, say, unaffected by terribly scenic top of estuary (7,7)

'geology say' is the definition.
(geology is a kind of natural science)

'unaffected by terribly scenic top of estuary' is the wordplay.
'unaffected' becomes 'natural' (synonyms).
'by' is a charade indicator (letters next to each other).
'terribly' indicates anagramming the letters.
'top of' suggests taking the first letters.
The initial letter of 'estuary' is 'e'.
'scenic' is an anagram of 'scienc'.
'natural'+'scienc'+'e'='NATURAL SCIENCE'