172 



KNOWLEDGE 



[Septembek 1, 1892. 



as per diagram A. That such an arrangement of " clefts " 

 as the above could have ever been " river beds," or due to 

 river action, is simply incredible, the more so, as many of 

 them traverse inclines athwart the drainage slopes, the 

 " gape " of the clefts being precisely what it should appear 

 if they were vast fissures, or marginal fractures of the 

 crust, "due to subsidence of the adjoining mare. Clearly, we 

 are not justified in ignoring all this evidence, derived from 

 the arrangement of the " clefts "' surrounding Serenitatis. 

 It is distinct and positive evidence against the view that 

 they are due to river action, and equally clear that they 

 are marginal fractures of the crust, due to the subsidence 

 of the enclosed sea ; In other words, a proof that the sub- 

 sidence of sea bottoms is a lunar as well as a terrestrial 

 phenomena. This type of arrangement is seen elsewhere, 

 as in Mare Humorum, and may be called type A. Another 

 type of arrangement, B, is at times seen, where two 



the floor, 

 who says 

 to exist 



mares are divided by what appears to be a .shoal, as 

 between Humorum and Nubium, over and along which a 

 large group runs more or less parallel to each other. 

 In this case (see diagram B) the group of clefts runs 

 parallel to and over what woiild be the " water parting " 

 which divides the two seas, an arrangement directly 

 opposed to the view that they are "river beds," but pre- 

 cisely that which we should naturally expect if the clefts 

 were due to subsidence of the marea on each side, east and 

 west. A third type of arrangement, C, is where we see the 

 clefts conspicuously forked and crossed, 

 S as in the walled plain Gassendi, at 



Ramsden, Triesnecker, &c. In these 

 cases it is equally difficult to understand 

 K .- how such clefts- could be regarded as 

 \ due to river action ; not only do they 



(o E cross each other in all directions, in a 

 / manner quite opposed to our experi- 



ence of terrestrial river beds, but in 

 the case of Gassendi the entire system 

 lies within the ring of the walled plain. 

 r' If, however, there has been an exten- 



sive subsidence, not only of Mare 

 Humorum to the south, but also of 

 on the north-west and west, and of the ring 

 to and around a rigid centre, or cluster of 

 peaks, such a comphcated series of fractures will be at 

 once intelligible. In the case of Gassendi, indeed, there is 

 remarkably good internal evidence that this view is 

 correct. It will be seen on reference to diagram C, drawn 

 mainly from Nelson's map of Gassendi, p. 337 of his 

 " Moon," that the ring of this formation is gapped in 

 two places on the southern border 1 and 2, and that 

 each of these gaps, or passes, coincides with the extremity 

 of a cleft on the floor inside ; also that the ring is gapped 

 in two [places, 3 and 4, on the western border, each 

 gap again coinciding with the extremity of a cleft on 



A'-'-' 



CASSEIVBI 



the mare 



itself, on 



This peculiarity was observed by Neison, 

 at p. 312, " Some connection appears also 



system and the peculiar 



C,«S5«'r,.Z; \\ 



>orrt 



between the riU 

 passes in the walls of the 

 formation." The connection 

 referred to seems to be this, 

 that the mareal subsidence 

 and displacement to the 

 south-west and west, which 

 opened the crevasses or clefts 



on the floor, in line with 1 , f/ l\___-'^'|fi'^ 

 2, 3 and 4, at the same time-^ l[ I /I \'"S i*"", 

 neci'fisitiilii gapped the ring at 

 these same places. This re- 

 markable coincidence, there- 

 fore, of the extremities of 

 clefts with gaps in the ring, 

 amounts almost to a de- 

 monstration that adjoining 

 mareal subsidence, involving, 

 as it necessarily must, some 

 little lateral displacement, has by the same operation both 

 cleft the fioor and gapped the ring. 



Thus in the foregoing, while we have seen in A, B 

 and C three quite distinct types of arrangement of the 

 " clefts," they have in all cases, on exammation, told the 

 same tale — /.<., that instead of being river beds, they are 

 fractures of the crust or fissures, due to adjoining mareal 

 subsidence. This view is indeed confirmed on a large 

 scale by the vast series of clefts, extending from Hyginus, 

 past Sabine, Censorinus, and Capella, as far as Goclenius, 

 which border the Marea Vaporum, Tranquilitatis, and 

 Fcpounditatis, and is also seen on a small scale in many 

 places. But there are occasionally instances wherein it is 

 not so easy to adduce " mareal subsidence " as a cause for 

 the cleft, yet easy to show that it cannot have been a river 

 bed. The great cleft of Sirsalis, for instance, which runs 

 in a fairly straight line, crosses hills, valleys, craters, and 

 mountain ranges quite impartially for some 400 miles, a 

 series of feats which no terrestrial river is ever likely to 

 accomplish. 



But quite apart from the evidence based on the 

 arrangement of clefts, we have in their forms alone fairly 

 good proof that they are fractures of the crust and not 

 river beds. As Proctor points out in his " Moon," page 

 176, they extend " with perfect straightness for long dis- 

 tances and changing direction (if at all) suddenly, there- 

 after continuing their course in a straight line." This 

 notorious peculiarity is utterly opposed to all our experi- 

 ences of terrestrial rivers, the sinuosities of which are well 

 known. But the straightness and angularity is what we 

 should naturally expect to see if clefts are fractures in a 

 tolerably thick, brittle, and semi-rigid crust, induced by 

 the subsidence of adjacent areas — they are not at all the 

 features we should expect to see either in a thin crust, or 

 one of open friable nature like sand or alluvium ; in the 

 latter we should certainly see a maze of short, irregular 

 reticulations, instead of the great length, straightness, 

 and angiilarity. 



But a smgularly conclusive and beautiful proof that the 

 " clefts " are fractures, or fissures in the crust, which pass 

 through an outer shell, down to moister and warmer sub- 

 strata, is seen in their frequent structural association with 

 small craterlets and crater cones. These are so often seen 

 at the angles, or jimctions of clefts, that they are ob- 

 viously due to some deeply-seated cause for unusual dis- 

 location of the strata. At times we see, as in Hyginus, 

 three or four ci'aters isolated along the cleft, in other cases 

 they may lie close together, the well-known " crater row," 



