Some fissures become apparent in a review of the White Horse Inn archway (8)
I believe the answer is:
crannies
'some fissures' is the definition.
('cranny' can be a synonym of 'fissure')
'apparent in a review of the white horse inn archway' is the wordplay.
'a review of' is a reversal indicator.
'apparent in' indicates the answer is hidden within the clue (the answer can be seen in the clue).
'seinnarc' is hidden in the letters of 'white horse inn archway'.
'seinnarc' back-to-front is 'CRANNIES'.
'become' acts as a link.
(Other definitions for crannies that I've seen before include "Small openings or crevices" , "Small narrow spaces" , "Nooks and crevices" , "Scanner I used to find nooks" .)