78 REPORT— 1869. 



photograms, at the S.W. end by the angle formed by the N.E. border of 

 HaJley. The posteriority of the epoch of the valley IV M 2?, lY A" ", and 

 IV A*^ 13 to that of Hind is strongly indicated by the continuity of the S.E. 

 slope of Hind being interrupted by the valley, much in the same way as the 

 N.E. is by the cliff IV A'' ^^. We may trace here with great probabUity the 

 following sequences of formations :— 1°, that of the highland IV A'' ^ ; 2", the 

 fault IV A" 23, lY A.^ 62 . 30^ the protrusion of Hind ; 4°, the formation of 

 the valley IV Ai ^7, IV A'' ^'^, IV A** ^^ (several valleys hereabout are nearly 

 parallel with this) ; 5°, the formation of the cliff IV A'' ^^ ; G°, the protrusion 

 of HcdUij ; and 7°, the cleft or wall on the E. of IV A'' 2, which is the highest 

 in the locality." 



"The exactitude of direction of certain lines of valleys and mountains on 

 opposite sides of HijypcircJms indicate a more recent epoch for the formation 

 of the floor of Hijyparclius than for the production of the valleys and moun- 

 tains on the lines specified. In connexion •with these circumstances the 

 following questions suggest themselves. Docs the general parallelism of the 

 lines of mountains and valleys in the neighbourhood of Hipjyarchus point to 

 contemporaneity of origin? Has the present floor of Hipparclius resulted 

 from a subsidence, by which the former surface was depressed below the 

 surrounding levels? There are some indications that, prior to the production 

 of the fault IV A" ", IV A^ -^, IV" "'-, the sm-faces E. and W. of it were at 

 the same level. Was this the level at which the valleys and mountains 

 above alluded to were continuous ? and has the sui'face between them, as well 

 as the floor of Hipparclms, generally become depressed below its former 

 level? If so, it would appear that Horrox was opened upon this former 

 irregular surface ; and it may be interesting to inquire further as to what 

 may have become of the portions of the mountains and valleys which have 

 disappeared. This question may be very difficult to answer, especially in 

 the very imperfect state of our selenographical knowledge." 



" There is some reason to believe that Horrox was not the only crater 

 opened on this part of Hipparclms previous to the supposed epoch of de- 

 pression. The curved mountain-chain IV M ^s presents all the characters of 

 an ancient and nearly filled crater, slightly exceeding Horrox in size. Nearly 

 half the ring is left, two craterlets are opened in the line of wall, and the 

 surface which is traversed by a cleft is slightly depressed below the level of 

 the surrounding floor of Hipparclms. It is one of those instances which 

 AVebb, in his paper on the Moon (Frasei''s Magazine, Sept. 1868), refers to 

 ' of cavities in proximity to the grey plains having interiors so flat, so grey, 

 so identical in appearance and level with the plain, that hardly a doubt 

 remains of their having been subsequently filled iip by intrusive matter of 

 the same origin and under the same pressure as that around them.' If 

 lY M 5^ be a nearly submerged crater, and the lines of mountains and valleys 

 on opposite sides of Hipparclms were once continuous, the intermediate 

 portions having also been submerged, the question to be resolved is — Whence 

 came the material which has effected the submergence ? The whole of the 

 floor of Hipp>arclms, as compared with the surrounding formations, strongly 

 exhibits indications of change of level ; it is comparatively smooth, and of 

 different reflective powers. The most striking difterence of level occurs near 

 the cliff IV A" i« and the mountains IV A^ -^ and IV A^ -t?. Does this at all 

 point to a subsidence of the floor of llipparchus, accompanied by an invasion 

 of intrusive matter ? Instances of subsidence may be found on the moon'; 

 Strain/Id ivcdl may be quoted, the surface on the E. being at a lower level 

 (about 1000 feet) than that on the W. The j)lain of Dionysius (Eeport Brit. 



