S. and S.E. is much broken by craters and depressions, the largest and
most conspicuous interrupting the continuity of its summit-ridge on the
latter side. A fine crater-row traverses the central part of the
interior, nearly axially, and a delicate cleft crosses the N. half of the
floor from the inner foot of the N.E. wall to a crater not far from the
opposite side. I detected another cleft on November 11, 1883, also
crossing the N. side of the floor.

South of Mersenius is the fine ring-plain Mersenius _d_, about 20 miles
in diameter, situated on the border of the Mare; and, extending in a line
from this towards Vieta are two others (_a_, and Cavendish _d_,),
somewhat larger, but otherwise similar; the more easterly being connected
with Cavendish by a mountain arm. One of the principal clefts of the
system (all of which run roughly parallel to the N.E. side of the Mare,
and extend to the Percy Mountains E. of Gassendi) crosses the floor of
_d_, and, I believe, partially cuts into its W. wall. Another, the
coarsest, abuts on a mountain arm connecting _d_ with Mersenius, and,
reappearing on the E. side, runs up to the N.W. wall of the other ring-
plain, _a_, and, again reappearing on the E. of this, strikes across the
rugged ground between _a_ and Cavendish _d_, traversing its floor and
border, as does also another cleft to the N. of it. Cavendish _d_
includes a coarse cleft on its floor, running from N. to S., which I have
frequently glimpsed with a 4 inch achromatic. There are two other
delicate clefts running from the Gassendi region to the S.W. side of
Mersenius, which are in part crater-rills.

CAVENDISH.--A notable ring-plain, 32 miles in diameter, S.E. of
Mersenius, with a prominently terraced border, rising at one point on the
S. to a height of 6000 feet above the interior, on which are a few low
ridges. A large bright ring-plain (_e_), about 12 miles in diameter,
breaks the continuity of the S.E. wall, and adjoining this, but beyond
the limits of the formation, is another smaller ring with a central hill.
There is also a bright crater on the N.W. border. The W. _glacis_ is very
broad, and includes two large shallow depressions. An especially fine
valley runs up to the N. wall, to the W. side of _e_.

VIETA.--One of the finest objects in the third quadrant; a ring-plain 51
miles in diameter, with broad lofty walls, a peak on the west rising to
nearly 11,000 feet, and another N. of it to considerably more than