Which preposition to use with formative

in Occurrences 1%

There was an enthusiasm and warmth distinguishing these early days of the Amoy church that were formative in a very high degree, and that are now a precious memory.

of Occurrences 1%

In the orations in question, these men proclaim the maxims adopted by their countrymen and formative of their own character; they record their views of their political relations and of their moral and spiritual nature, and publish the principles of their designs and conduct.

Which preposition to use with  formative