We are told of Roger moving towards Sam'n'Eric as one 'weilding a nameless authority'. What is this, and why is it nameless?

Throughout the novel, Roger's actions show him to be a boy who is the first to break with civilization.  He is the first to throw rocks near a lilun, the first to stab a piglet, and the first to take a cheap shot against Piggy.  The nameless authority that Roger wields is violence.  He has no qualms about picking on the smaller children and torturing Sam'n'Eric to get the knowledge he wishes from them.  If you're not willing to go so far as to call his authority violence, it is, at absolute least, self-assuredness.