Which preposition to use with firma

of Occurrences 4%

In this flat swamp of convalescence, left by the ebb of sickness, yet far enough from the terra firma of established health, your note, dear Editor, reached me, requestingan article.

after Occurrences 1%

We spent a day in driving about Bordeaux, enjoying the mere fact of restoration to terra firma after twelve days' imprisonment on the ocean.

Which preposition to use with  firma