"A briar cradle rocks its babe to sleep
Its contents watched by Sycorax"
Instead of the Sycorax most likely referred to in the song (an African witch from Shakespeare's The Tempest), this is the Uranian moon (named after said witch). The "babe" is Caliban (Sycorax's son in The Tempest), and his "briar cradle" happens to be a briar pipe.
Hope you like.