MOON, RECENT OBSERVATIONS AND STUDY OF THE. 



589 



derlie the surface equally everywhere, forming 

 a separation of equal thickness at all points be- 

 tween the solidifying globe inside and a shell 

 of equal thickness outside. Hence, when a 

 racture occurred, the crust would instantly 

 jive way to the right and left, and the rush of 

 the imprisoned waters toward the exit would 

 upheave the side that offered the least resist- 

 ance to its force, and ranges like the lunar Ap- 

 ennines would result, where one face is a long, 

 gradual slope, and the other rises abruptly 

 from a plain. Mountain-chains of this char- 

 acter would form the boundaries of the great 

 plains to a large extent, because the water 

 released in the locality of such an upheaval 

 would permit the crust it had supported to 

 sink to the bottom, so that less of the upheav- 

 ing action would occur in those locations than 

 elsewhere. Hence it is that such mountain- 

 ranges are found on the borders of the great 

 plains of the moon, which present surfaces 

 so level as to be suggestive of their identity 

 as part of the original surface of the globe 

 in its primal condition of aggregation, preced- 

 ing the period when the crust was fractured 

 by upheaval. No great ring-mountains are to 

 be found on those plains, though the smaller 

 sizes are not infrequent, showing that the pe- 

 riod of the upheaval of the ring-mountains, 

 which next followed, did not extend its forces 

 over those plains. 



The forcible exit of the water would be lit- 

 tle more than local ; because those on the oth- 

 er side of the globe, being 3,000 miles away, 

 would not even be affected by the disturbance 

 before the means of exit would be again closed 

 by the sinking back of the upheaved masses 

 as they were relieved by the release of the wa- 

 ter from beneath and the up-rush of the plastic 

 earths into the fractures, thus again sealing 

 the exit of the water still within the globe, 

 and again compelling it to put forth fresh ef- 

 forts of upheaval to effect still other exits from 

 within. Meantime, the contact of the water 

 with the inside of the crust would be gradu- 

 ally thinning it, while the slow compacting of 

 the body kept steadily increasing the pressure 

 upon the water, and the period of mountain- 

 chain upheavals would merge into a secondary 

 character, more local in its phases, because by 

 this time the under side of the crust, and the 

 upper side of the mass within, would be in con- 

 tact in many places, and particularly beneath 

 the localities where the upheaval of the mount- 

 ain-chains had largely released the immediately 

 underlying water, and thereby present a fur- 

 ther accumulation of water, and consequently 

 a partial exclusion of the forces of upheaval 

 from these regions. Hence the relatively small 

 numbers of ring-mountains to be found upon 

 the plain. In fact, there were none until after 

 the epoch of the upheaval of the great ring- 

 mountains had passed away and been succeed- 

 ed by the formations of those of smaller di- 

 mensions. 



After the crust and the interior mass had 



come in contact in different places, the still 

 imprisoned waters would be separated by those 

 local barriers, and could only concentrate their 

 upheaving energies in localities most favorable 

 to their assembling by the increasing pressure 

 of the slowly contracting globe. The stratum 

 of water beneath the incrusted surface, being 

 no longer continuous about the interior globe 

 and inside the external shell, but separated by 

 their junctions at different points, would neces- 

 sarily be confined to less extended areas of ac- 

 tion than formerly. So we have, as the suc- 

 ceeding stage of upheaval, mountain - ranges 

 more or less irregularly oval or circular, but 

 inclosing plains of considerably greater extent 

 than the almost exactly circular ranges that 

 were evidently upheaved at a later date. 



The nature of the mechanical action that up- 

 heaved the ring-mountains does not seem to 

 be difficult of solution. When the sinking of 

 the external crust and the interior globular 

 mass became more extended, the intermediate 

 assemblages of water would be confined to a 

 more limited extent of action. The force of 

 upheaval would be greatest at the center of 

 the location that was being upheaved, the sur- 

 face thxis becoming convex, and the convexity 

 spreading until the crust would fracture ; then 

 the outrush of the water relieving the pressure 

 within would cause the convex upheaved sec- 

 tion to fall back into the chasm, and the weight 

 of this dome being thus suddenly thrown upon 

 its circumference, the fracture would chiefly 

 take place there, and the groins of the dome 

 be upheaved similar to what occurs when the 

 groins of a flat arch yield under analogous cir- 

 cumstances. Hence the origin of the ring- 

 mountains. The dome-section would sink to 

 the bottom, retaining more or less of its con- 

 vexity ; and, therefore, many of them form 

 convex plains. The upheaved mountain at the 

 center" being due to the yielding, also, at that 

 locality, in all likelihood, after the superincum- 

 bent mass began to sink (for the resistance 

 offered by the waters beneath would then be 

 all directed to its center), the duration of the 

 overflow or its volume would depend upon the 

 manner in which it was connected with the 

 water-supply of the interior. The far greater 

 number of the ring-mountains present the ap- 

 pearance of having had little or no water-sup- 

 ply beyond that which upheaved and con- 

 structed them, while the few examples like 

 Tycho, judging by their surroundings, must 

 have had a vast supply and a long-continued 

 overflow. 



The plains of the moon appear in the tele- 

 scope very little darker than other portions, 

 though they show very dark in a photograph. 

 If a photograph of our earth were made from 

 the moon, all the portions that were covered 

 with vegetation would be presented in exactly 

 the same manner ; but when seen by the tele- 

 scope they would be very little darker than 

 other parts, because vegetation absorbs the 

 kind of light that produces the photograph, 



