Not all Spanish galleons that are found to contain treasure. ??
The original sentence was "Not all Spanish galleons that are found contain terasure" T thought there were double verbs, "found" and "contain". So, I changed the sentence become
"Not all Spanish galleons that are found contain treasure"
Then I realized, that was not a double verbs, "found" is a part of preposition of "Not all Spanish galleons that are found" which is the Subject. So the sentence need a verb "contain", not "to contain", because "to contain" is to infinitive which is can be a Subject too.
Does my argument right?