Where were allusions in 'Macbeth'?

In Act 2 Scene 3, Macduff says:

Approach the chamber, and destroy your sight

With a new Gorgon.

The Gorgon was a Greek monster who would turn you into stone if you looked at it.

Also, in Act 3 Scene 5, Hecate says:

And at the pit of Acheron

Meet me i' the morning

Acheron is a river in Greece which was believed to flow through the underworld. However, these Words were probably not written by Shakespeare, but rather by Middleton.

All of the other Classical allusions in the play ("Neptune's ocean" etc.) were to Roman rather than Greek mythology.