[Mojave]

those are basis for the formal laws

Formal laws? You mean statutes?

Statutes aren't common law.

Read a book.

[jf55510]

No, but judicial opinions are the basis of common law because the judges who wrote the opinions brought in local customs, practices, etc. to bring into a workable system. So therefore, the judges made the common law.

[Republican Party Reptile]

Again, from your own quoted text "As we have seen the basis of Common Law was ..." ... why bother distinguishing "the basis of Common Law" if the local customs by themselves already equal to Common Law. It should just straight forward said "Common Law was ..."