You arrive inside the Fire Marble Dome on Catherine's island. Press the button on the floor to the right of the book to lower the book stand and open the dome. Turn and follow the walkway toward a gigantic tree stump covering the entire small rocky island. Go up the stairs and through a door to an elevator. Note three keys and a lever, plus a pull cord. Press the keys and listen to the different sounds. Enter the correct sequence of sounds (the ones from the metal sphere in Gehn's bedroom) and then throw the lever to open the cage. Catherine joins you and pulls the elevator handle to descend. She congratulates you. She tells you to open the fissure and reminds you that the combination is in her journal. Go back to Gehn's age. You'll have to stop the dome again because Catherine just used it.
