Find a French soil (7)
I believe the answer is:
Here is my best explanation:
'find' is the definition.
(unearthing is a kind of finding)
'a french soil' is the subsidiary indication.
'a french' becomes 'un' ('a' transated into the French language).
'soil' becomes 'earth' (I've seen this before**).
(Other definitions for unearth that I've seen before include "Exhume", "Dig up or find for haunter", "Expose", "Excavate, dig up", "Dig up - uncover", "Disclose", "Discover", "Bring out of obscurity", "Disinter" and "Find by digging".)