These streaks are cracks, made in the Moon's surface by cooling or by shrinkage, through which volcanic matter has been forced up by internal pressure.

The sinking ice of a frozen lake, when meeting with some sharp pointed rock, cracks in a radiating manner: every one of its fissures then admits the water, which immediately spreads laterally over the ice pretty much as the lava spreads itself over the lunar surface.

This theory accounts for the radiating nature of the streaks, their great and nearly equal thickness, their immense length, their inability to cast a shadow, and their invisibility at any time except at or near the Full Moon.

Still it is nothing but a theory, and I don't deny that serious objections may be brought against it." "Do you know, dear boys," cried Ardan, led off as usual by the slightest fancy, "do you know what I am thinking of when I look down on the great rugged plains spread out beneath us ?" "I can't say, I'm sure," replied Barbican, somewhat piqued at the little attention he had secured for his theory.
"Well, what are you thinking of ?" asked M'Nicholl.
"Spillikins!" answered Ardan triumphantly.
"Spillikins ?" cried his companions, somewhat surprised.
"Yes, Spillikins! These rocks, these blocks, these peaks, these streaks, these cones, these cracks, these ramparts, these escarpments,--what are they but a set of spillikins, though I acknowledge on a grand scale?
I wish I had a little hook to pull them one by one!" [Illustration: AN IMMENSE BATTLEFIELD.] "Oh, do be serious, Ardan!" cried Barbican, a little impatiently.
"Certainly," replied Ardan.

"Let us be serious, Captain, since seriousness best befits the subject in hand.