crossed each other; those entered craters and came out at
the other side. Here, they furrowed annular plateaus, such as
_Posidonius_ or _Petavius_. There, they wrinkled whole seas, for
instance, _Mare Serenitatis_.

These curious peculiarities of the lunar surface had interested the
astronomic mind to a very high degree at their first discovery, and have
proved to be very perplexing problems ever since. The first observers do
not seem to have noticed them. Neither Hevelius, nor Cassini, nor La
Hire, nor Herschel, makes a single remark regarding their nature.

It was Schroeter, in 1789, who called the attention of scientists to
them for the first time. He had only 11 to show, but Lohrmann soon
recorded 75 more. Pastorff, Gruithuysen, and particularly Beer and
Maedler were still more successful, but Julius Schmidt, the famous
astronomer of Athens, has raised their number up to 425, and has even
published their names in a catalogue. But counting them is one thing,
determining their nature is another. They are not fortifications,
certainly: and cannot be ancient beds of dried up rivers, for two very
good and sufficient reasons: first, water, even under the most favorable
circumstances on the Moon's surface, could have never ploughed up such
vast channels; secondly, these chasms often traverse lofty craters
through and through, like an immense railroad cutting.

At these details, Ardan's imagination became unusually excited and of
course it was not without some result. It even happened that he hit on
an idea that had already suggested itself to Schmidt of Athens.

"Why not consider them," he asked, "to be the simple phenomena of
vegetation?"

"What do you mean?" asked Barbican.

"Rows of sugar cane?" suggested M'Nicholl with a snicker.

"Not exactly, my worthy Captain," answered Ardan quietly, "though you
were perhaps nearer to the mark than you expected. I don't mean exactly
rows of sugar cane, but I do mean vast avenues of trees--poplars, for
instance--planted regularly on each side of a great high road."

"Still harping on vegetation!" said the Captain. "Ardan, what a splendid
historian was spoiled in you! The less you know about your facts, the
readier you are to account for them."

"_Ma foi_," said Ardan simply, "I do only what the greatest of your
scientific men do--that is, guess. There is this difference however
between us--I call my guesses, guesses, mere conjecture;--they dignify
theirs as profound theori