St. Augustine said: "For, if the order of succession of bishops is to be considered, how much more surely, truly and safely do we number them from Peter, to whom, as representing the whole Church, the Lord said: 'Upon this rock I will build my church and the gates of hell shall not prevail against it' (Mt. 16:18)."
-A8
Yes. But in that quote, he does not say that Peter is the Rock. In the quote I gave from Augustine, Peter is NOT the Rock. Christ is the Rock, and Peter's confession was key - not Peter himself.