ON MAPPING THE SURFACE OF THE MOON. 23 
gently sloping character, are directed towards W. by N., and in “ Full Moon” 
the line is seen as a “ Ray” from “ Tycho.” See letterpress, areas IV A‘, 
IV AS, pp. 31 and 32, and Report Brit. Assoc. 1866, pp. 267, 268. Neither 
B. & M. nor Lohrmann give this line of cliffs. 
The N.E. line of cliffs (direction N.W.—S.E.) is a portion of a somewhat in- 
terrupted line which extends from the EK. border of Ptolemeus to a mass of 
high land E. of Agrippa. In crossing the Terra Astronomica from the W. 
border of Herschel, it is slightly curved, the convexity being towards the 
§.W. and the faces of the cliffs towards the N.K. The altitude may be about 
equal to the lower portions of the mountainous border of Ptolemeus. It is 
very imperfectly represented on B. & M.’s and Lohrmann’s maps, but it may 
be traced on Lohrmann’s Sec. I., although the character of a range of cliffs 
is not given. Passing along the range from Herschel towards the N.W., we 
find it first cut through by the valley III A*? IIT A$?; and parallel with this 
valley on the N.W. is a short mountain-arm, which springs from the line of 
cliffs, and probably forms the highest part of the boundary of the valley on 
the N.W. Itis next cut by a “fault,” IIT A%8 and III A$, which will be 
hereafter described. Just W. of this “fault” is the crater IV A*® III A* 1, 
which is situated on the line of cliffs and appears to be its culminating 
point. From thence the line is continued to the 8. edge of Reawmur, and 
merges into the S.W. and W. border of Reaumur, of which IV A%5 is the 
highest point. From the W. border of Reawmur the crater IV A*4 appears 
to connect it with the short mountain-chain IV A*", which joins the S.E. 
border of Rheticus. This line of cliffs is more strongly marked on the 
photogram than the boundary of Hipparchus, as shown by B. & M. and 
Lohrmann. 
Mountains.—The isolated mountains on this formation are but few; the 
most important are [V A¢ 8° and IV A$! on the subformation IV A$ 25, The 
remainder are either cliffs or mountain-borders of depressions and plains. 
Plains.—Three distinct plains may be specified as occurring on this forma- 
tion—Lohrmann’s W, Sec. I., Reawmur, and the small plain N.E. of it. They 
are all surrounded by mountain-borders. To these may be added the S.W. 
part of Hipparchus, W. of the westerly line of cliffs, which is the most level 
part of the formation. 
Depressions.—The most remarkable and important of these is the valley 
Til A*? IIT A¢?, N.W. of Herschel, crossing the N.E. line of cliffs ; and next 
is LY A*10, which is fully described under the symbols IV A*!°, TV A*# in 
letterpress to areas IV A*, IV AS, pp. 14 & 17, and Report, Brit. Assoc. 1866, 
pp. 250 and 253. IV A*!, IV A*!5 may also be included. In addition a 
large depression, IV A‘ !*?, is found between two ridges, which extend from 
TV A*7 and IV A*?S to TV A$ *°, It is well shownin De La Rue’s photogram 
of Feb. 22, 1858, and another, [V A¢ 9, between the crater IV A$1 and the 
mountains IV A¢ *7 and IV A$ &, 
The most remarkable subformation on Terra Astronomica is ITV A$ %, a 
careful description of which will be found under its symbol in letterpress 
to areas LV A“, IV AS, pp. 24 and 25, and Report of British Association, 1866, 
p- 261. 
Faults.—In addition to the “fault”? on the W.N.W. boundary, a remark- 
able one, III A*® Til A$15, extends from the N.W. border of Ptolemeus to the 
E. border of Reawmur. It crosses the space between Ptolemeus and the 
plain IV A*® IIT A*7 TIT AS 14 IV As *4 (W, Lohr. Sec. I.), grazes the S.W. 
extremity of the valley III A*? III As 2, N.W. of Herschel, and then traverses 
the plain, just grazing the E. edge of the crater III A*!, where it cuts the 
