area, the Syrtis Major, and, below the one in longitude 270°, the Syrtis Minor. This correlation was highly suggestive in itself. As if, however, to remove all question as to possible coincidence having a hand in the matter, the agreement in position was emphasized by visible connection. Two long dark streaks appeared joining respectively each bay to its corresponding Syrtis.
But the most significant fact about the band was that it kept pace with the polar cap's retreat toward the pole. As the white cap shrank it followed pari passu so as always to border the edge of the snow. It thus showed itself not to be a permanent marking of the planet's surface, since it changed its place, but a temporary one, dependent directly upon the waning of the cap itself. In short, it was an associated detail, and itself instantly suggested its character, namely, that it was water at the edge of the cap due to the melting of the polar snow.
Not only did the band conform with the cap in position; it did so in size. As the snows dwindled, the blue band about them shrank in width to correspond. By August it was a barely discernible thread drawn round the tiny white patch which was all that remained of the enormous snow-fields of some months before. Finally, on October 13, when the snow entirely disappeared, as we shall presently see, the spot