rgest of the three, being over seventy miles in
diameter, and its highest peak is 16,500 feet in altitude.

I should have liked to have shown them the splendid double-walled plain
called Petavius, which has a convex floor some 800 feet higher in the
centre than at the edges. We were, however, too late both for that and
Langrenus, another fine formation on the same meridian, for the sun had
set upon them and they were in darkness, so it was no use going any
farther in that direction.

We now directed our course over the Sea of Clouds till we arrived at
what is known as the "Straight Wall."

"M'Allister," I said, "that ought to interest you, for there is a
somewhat similar formation in Scotland. You see this is an escarpment,
or cliff, over sixty miles long, and varying from about 600 feet to 900
feet in height.

"This cliff is one of the best known examples on the moon of what in
geology is termed a 'fault,' indicating either that one part of the
general surface has been greatly elevated, or that the adjoining part
has been depressed. We have many examples of such 'faults' on the
earth--for instance, one runs a long way across Scotland, from
Stonehaven round to Helensburgh, between the Highlands and the Lowlands,
and is about 120 miles in length. That is about twice the length of the
Straight Wall; so you see that Scotland can beat the moon in that
respect!"

This brought M'Allister up to the scratch. "Scotland," he exclaimed
excitedly, "can hold her own in most things! Why, mon, the empire is
indebted to her for the finest statesmen, the cleverest lawyers, the
best engineers and scientists, and, allow me to say, the bravest
soldiers in the whole world! Scotsmen go everywhere, and can do
anything!"

"Oh yes, M'Allister," said John, with a laugh, "and a Scotsman has got
to the moon! but, please, do not forget that two Englishmen planned the
trip, and devised the means of accomplishing the journey!"

M'Allister smiled a rather wintry smile, and then subsided. John was a
bit too smart for him that time.

Passing on, we inspected the large cleft running parallel to the
Straight Wall, and the small mountain close by named after Birt, the
well-known selenographer. We then crossed the Sea of Clouds again, and
had a long look at the great system of straight clefts near Campanus and
Hippalus, together with the fine walled plain Gassendi, the floor of
which is at some parts 2000 feet above the lunar surface. I had often