22 REPORT—1868. 
wards Hipparchus impart a somewhat curvilinear form to the boundary here- 
about. From the N.E. end of IV A” 4, which lies in the depression IV A” 21, 
as far as the E. edge of the crater IV Af 4, the boundary is nearly rectilinear 
and nearly coincident with the “fault” IV A"", IV A® 20, TV A* ?, which, 
probably originating in the crater IV A”?, has either elevated the surface on 
the W. or depressed the surface of the W. portion of Hipparchus, so that it is 
considerably below the high land; between IV A® 1 and LV A* !4 this high land 
rises into the peaks IV A? #8 and IV Af 47, At the crater IV A | this portion 
of the boundary forms a very obtuse angle with the valley [TV A8*! Ty A* 77, 
which extends as far as the N. end of IV A*1°. Here the boundary becomes 
indistinct. Beer and Midler, who do not give the “ fault” nor the valley, 
show the boundary as turning E. at TV A 4, passing the cliff or mountain 
IV A“ at the S. end of IV A*%!°, and passing along the depressions [TV A* ? 
and ITV A*}3 (neither of which they show), proceeding to the crater IV A*7, 
and further continued parallel with the W. mountainous border (LY As 47) 
of IV A¢24, Lohrmann’s W, Sec. I., through the crater IV A¢® to or near 
the small crater [V A¢*3. The dotted line shows the approximate direction 
of the N. and §.E. boundaries as given by B. & M. and Lohrmann. Lohr- 
mann in Sec. I. indicates, although not very distinctly, the “fault” and 
valley. 
The N. and §.E. boundaries of Hipparchus, as laid down by B. & M. and 
Lohrmann, are by no means so distinct on the photogram as shown on the 
map and section. The natural boundary of the large formation Terra As- 
tronomica appears to be continued from the junction of the valley TV A*%t 
TV A“ 77 with the “fault” IV A" TV A8 20 LV A*”, along the higher land 
between the valley and Rheticus, through the 8.E. mountainous border of 
Rheticus to the N.E. angle of Rheticus N. of the equator; it then trends 
E.S.E. along the S.W. border of the Sinus Medii to the N. border of the little 
plain N.E. of Reawmur. From thence it trends E. to the mass of high land 
on the N.W. border of Lohrmann’s U, Sec. I., IIL A*!, the W. border of which 
carries it on to the circular “ tableland” III A* °, N. of Herschel; the W. edges 
of this “‘ tableland” and Herschel bring us to the N. of Ptolemeus, the N.W. 
border of this walled plain being common to Ptolemceus and Terra Astro- 
nomic. 
Within the boundary now traced out, a more or less individualized forma- 
tion will be found; and as no part has received a distinct name except the 
S.W. (“ Hipparchus”’), the whole may not inappropriately be termed “ Terra 
Astronomica.” 
Inrertork Formatrons.—These may be characterized as Cliffs, Lines of 
Upheaval, Mountains, Plains, Depressions, Faults, and Craters. 
Cliffs—Two well-marked lines of cliffs cross the Terra Astronomica in 
divergent directions from the N.W. angle of Rheticus. They are both di- 
stinct on the photogram. 
The W. line of cliffs from the N.W. angle of Rheticus, along its W. border, 
passes W. of IV A*!, through the W. part of Hipparchus, past the prominent 
cliff [TV A$ ®8 (where the curved chain IV A$ ®* branches from it) towards the 
space between LV A$ 27 and IV AS 28, through the middle of TV As, to TV As %6, 
on the N.E. border of Albatcgnius. Leaving Hipparchus, this line of cliffs 
crosses the N.E. part of Albategnius, and terminates on the E. border of the 
crater IV A+, on the E. of Albategnius. The faces of these cliffs are of a 
4 The lines of upheaval and depression upon areas IV A%, TV AS are tabulated and de- 
scribed in the letterpress to those areas, pp. 33 to 39, and Brit. Assoc. Report, 1866, 
pp. 269 to 275. 
