Mr. Stranger's sealed packet

Mr. Stranger flies to Mars in an armored spaceship. He finds it to be habitable, with majestic oceans and teeming with life. The Martians, blue and very much Victorians, call themselves the Grensum. Mars also has barbarians, called the Dergdunin; Stranger engages them with his ship. He eventually marries a Martian and brings her back to Earth.