skirts the floor of Parry on the E.

BONPLAND.--A ruined walled-plain with a low and much broken wall, which
on the S.W. appears to be an attenuated prolongation of that of Parry. It
is of the linear type, the formation approximating in shape to that of a
pentagon. The floor is crossed from N. to S. by a fine cleft which
originates at a crater beyond the S. wall, and is visible as a light
streak under a high light. Schmidt shows a short cleft on the W. of this.

FRA MAURO.--A large enclosure of irregular shape, at least 50 miles from
side to side, abutting on Parry and Bonpland. In addition to the cleft
which crosses it, the floor is traversed by a great number of ridges, and
includes at least seven craters.

THEBIT.--A fine ring-plain, 32 miles in diameter, on the mountainous W.
margin of the Mare Nubium, N.E. of Purbach. Its irregular rampart is
prominently terraced, and its continuity on the N.E. interrupted by a
large deep crater (Thebit A), at least 9 miles in diameter, which has in
its turn a smaller crater, of about half this size, on its margin, and a
small central mountain within, which was once considered a good optical
test, though it is not a difficult object in a 4 inch achromatic, if it
is looked for at a favourable phase. The border of Thebit rises at one
place on the N.W. to a height of nearly 10,000 feet above the interior,
which includes much detail. The E. wall of Thebit A attains the same
height above its floor, which is depressed more than 5000 feet below the
Mare.

BIRT.--This ring-plain, about 12 miles in diameter, is situated on the
Mare Nubium, some distance due E. of Thebit. It has a brilliant border,
surmounted by peaks rising more than 2000 feet above the Mare, and a very
depressed floor, which does not appear to contain any visible detail. A
bright crater adjoins it on the S.W., the wall of which at the point of
junction is clearly very low, so that under oblique light the two
interiors appear to communicate by a narrow pass or neck filled with
shadow. I have frequently seen a break in the N.W. wall of Birt, which
seems to indicate the presence of a crater. There is a noteworthy cleft
on the E., which can be traced from the foot of the E. wall to the hills
on the N.E. It is a fine telescopic object, and, under some conditions,
the wider portion of it resembles a railway cutting traversing rising
ground, seen from above. It is visible as a white line under a high
light.

THE STRAIGHT WAL