ON MAPPING THE SURFACE OF THE MOON. 33 
TY Af & of TV Af U is the E. of the two low ridges of Lohrmann. Between 
this and his 63, Sec. I., is the depression IV A* *, not shown by him ; and in- 
stead of a plain and central mountain between the ridge [TV Al and IV A 229 
TV A* *2, the S. part of the space is filled with the crater IV A? 1’, and the N. 
part dips to the N. angle of the formation IV A® "and I A8 0” (see [TV Af 11), 
—[W. Rk. B. 
My The AoW. part of the fault IV A"*3 TV AF. Direction $.S.E.— 
N.N.W., face towards E.N.E. 
This fault is nearly coincident with the “ray from Tycho” on which 
Bessel is situated. It takes its rise on the E. border of Hind, and passes, but 
does not obliterate, the narrow valley LV A"18. From the §.W. end of the 
valley IV A"®, which is on the lower level E.N.E. of the fault, to the long 
narrow valley or cleft* IV A”! (crater-rill No. 362 of Schmidt), where it in- 
tersects but does not divide the fault [TV A”! TV A®?9 TV A* ? (see letter- 
press, areas IV A*, LV AS, p. 20, and Report Brit. Assoc. 1866, p. 256), it 
is nearly coincident with the W. border of Hipparchus. The surface has 
been greatly disturbed near the point of junction of this fault with the fault 
Ty A”11 Ty A&20 TY A*?, in such a manner as to indicate that the force 
which produced IV A”!! TV Af 9 TY A*® has been exerted at an epoch 
more recent than that which produced IV A"*3 TV Af. It is in this dis- 
turbed locality that the craters [IV A? 19 and IV Af?! have been opened. 
After grazing the W. wall of IV A®!%, the fault IV A’?3 IV Af” passes 
onward by the W. wall of the depression IV A# 18, just W. of the crater 
2 Tt has been decided, upon mature consideration, to substitute the term “ cleft’ for 
“rill” as being more significant and comprehensive. It may be important to mention 
that a “cleft” differs from a “fault” in one essential particular; for example, a “ fault” 
marks a line of dislocation, which in some instances is characterized by an elevation of the 
surface on one side, and a depression on the other without presenting the appearance of a 
erack or narrow valley. In other cases, long narrow depressions may be found, mostly in 
lines of fault, and often in the same line with cliffs which have been upheaved probably by 
the same agency, and near the same epoch at which the narrow valley or “ cleft”? has been 
produced. ‘The term “fault” is consequently employed to signify the result of a force 
apparently acting in many instances more or less in radial lines from a centre or focus of 
disturbance, such as Tycho, from which numerous lines of “fault” diverge (see Report 
Brit. Assoc. 1847, p. 61), while the term “ cleft” is used to signify a partial result only, and 
one which has been manifested in depression as contradistinguished from elevation. (See 
‘Intellectual Observer,’ No. LX VII. August 1867, vol. xii. p. 52 e¢ seg. for some interest- 
ing remarks on Lunar Clefts by the Rev. T. W. Webb.) 
~ It may be well here to quote Sir C. Lyell’s definition of a “fault” as used in geologi- 
eal language, ‘ Principles of Geology,’ ninth edition, 1853, (Glossary) p. 805. “ Fault, in 
the language of miners, is the sudden interruption of the continuity of strata in the same 
Big accompanied by a crack or fissure varying in width from a mere line to several 
eet.” 
It is clear that the signification of the term “fault,” as applied to the moon, cannot be of 
precisely the same nature as when it is used in geology; for we cannot observe “ faults ’of 
this kind. Nevertheless the general principle holds good, viz. the elevation or depression 
of the surface plane on one side of the Lunar line of fault. Tt has been recognized as a 
peculiarity of geological “faults,” that the higher portions of the dislocated beds are 
usually on the sides towards which the “ faults” incline in ascending (Report Brit. Assoc, 
1847, p. 62), so that the ends of the raised strata present steep escarpments towards the 
depressed portions—phenomena of frequent occurrence on the moon’s surface. In the 
areas already mapped, we have the escarpments of the cliffs facing the lower level TV A@!1, 
the level of the floor of Hipparchus heing nearly identical with the summits of the cliffs (see 
letterpress to areas IV A* and IV A$; pp. 12, 13, and Report Brit. Assoc. 1866, pp. 248, 
249)—also the steep escarpments of the mountains between IV A®!® and IV Af 14 facing 
the floor of Hipparchus, while the general level W. of the mountains is much higher than 
the floor on the E. Numerous other examples may easily be given. Dislocations of 
mountains and craters are very apparent on lines of “ fault.” 
