32 



KNOWLEDGE 



[February 1, 1893. 



lava. Thus the Monte Sumna, which partly surrounds 

 Vesuvius, is steep on the inside towards the present cone, 

 and it slopes away gently on the outside. On the moon 

 we have many such volcanic rings. The lunar crater 

 Archimedes (shown on the lower right hand side of our 

 plate) is surrounded by an elliptical ring which is steeper 

 on the inside than on the outside. 



The question whether the lunar Apennines are similar 

 in character to terrestrial mountain chains, or whether 

 they form a part of a vast ring of volcanic origin which 

 once surrounded the Marelmbrium, is one which has very 

 important bearings on the theory we are led to adopt 

 with regard to the early history of the moon, and also 

 with regard to the early history of the earth. 



If the Mare Imbrium is not an ancient sea bed, but is 

 the floor of an immense volcanic crater, the lunar 

 Apennines must be very old, probably far older than any 

 terrestrial landmarks, for they must have been raised at a 

 time when the moon was hot enough to pour forth a sea of 

 lava which covered a seventieth of the entire lunar 

 surface — a sea which must have glowed with a red heat, 

 when the lava was liquid enough to flow evenly over the 

 entire area of this titanic crater, forming a spherical bed. 

 For the floor of the Mare Imbrium, as well as the floors of 

 the other great lunar planes, are all curved, and they appear 

 to correspond with the spherical curvature of the lunar 

 surface. 



The even curvature of the floor of the Mare Imbrium 

 will be recognized in our plate. The sun has risen high 

 upon the western side of the Mare, but the eastern side of 

 the floor is only just emerging gradually from darkness. 

 Many of the large lunar craters have similar flat sea-like 

 areas within them. TJuis Archimedes, the crater referred 

 to above, has a level floor some fifty miles in diameter, 

 and some seven himdred feet above the level of the 

 surrounding Mare Imbrium. Other lunar craters have a 

 flat floor and a central peak or mountain, but the Mare 

 Imbrium has no central elevation, nor have any other of 

 the lunar maria, though they are all more or less circular 

 or elliptical in outline. The circular walls of the lunar 

 craters are very fi'equently terraced on their inner and 

 steeper side as if there had been a tendency for the crater 

 edge to slip down in parallel ridges, or as if there had been 

 many ebbings and flowings of the lava sea within, leaving 

 terraces at different levels. But the precipitous south- 

 eastern declivity of the lunar Apennines does not exhibit 

 such terraces, and it is much more irregular in outline 

 than the rings which surround the majority of lunar 

 craters. In order to realize the uneven character of the 

 steep south-east front of the lunar Apennines the reader 

 should compare the curving white projections shown in the 

 plate published with this number with the beautiful pictures 

 of the same region taken by the Brothers Henry, which 

 were published in the December number of Knowledge for 

 1890, and -with the lunar photographs taken at the Lick 

 Observatory, published in Kno\\xedge for October, 1889. 

 It wiU be seen that the north-eastern side of this mountam 

 range is much notched and broken into projecting promon- 

 tories capped by peaks of very unequal altitude. The 

 loftiest of these summits is known as llio/fii-ns. It rises, 

 according to Neison, to a height of 18,000 feet, and accord- 

 ing to Mildler to a height of 20,900 feet above the plain 

 below. Its long straight edged shadow may be seen in our 

 plate stretching to a distance of rather more than fifty 

 miles across the Mare Imbrium. At the summit of this 

 lofty peak is a minute crater, not discernible in the photo- 

 graph, but easily seen under favourable circumstances with 

 the telescope. To the north-west is another lofty peak 

 known as Bradley, which reaches a height of 18,000 feet. 



Along the south-eastern flank of the lunar Apennines 

 is a somewhat broken range of lower hills such as would 

 be called foot-hills in the Rocky Mountain region of North 

 America. A little further to the south-east, and just 

 catching the rays of the rising sun, is a nai-row wall, 

 parallel to the general backbone of the Apennine range. 

 This is one of the narrow walls or ridges on the moon 

 which has been referred to as being possibly an immense 

 terminal moraine built up of rocks brought down during a 

 glacial epoch. If such a theory could be supported, it 

 would prove that the moon must have possessed, since the 

 raising of the Apennine range, an extensive atmosphere as 

 well as a considerable supply of water. But this ridge 

 does not seem to me to have the characteristics of a glacial 

 moraine which, in terrestrial mountain regions, generally 

 stretch across a valley in a curve that is concave towards 

 the hills from which the glacier that built the moraine 

 descended. With a higher sun, this curious ridge takes 

 the appearance of a very narrow bright line joining two 

 small craters. Whether some of the smaller ridges across 

 lunar valleys, which were pointed out by Prof. Frankland 

 as due to glacial action, are terminal moraines, I am 

 not prepai-ed to say. The lunar Apennines appear 

 so much more rugged than the formations which are 

 apparently more recent, that one would be inclined to 

 believe that time brings about a change in the form of 

 lunar mountains. But the change need not necessarily 

 have been brought about by the carving action of ice and 

 water. The volcanic vents that one sees in various parts 

 of the lunar Apennines, must have done something to 

 increase the irregularities by the addition of matter ejected 

 from below ; and the earthquakes which accompany such 

 eruptions would no doubt tend to shake down the softer 

 and weaker portions of the range. As we learn more of 

 the history of our own mountain ranges, we may learn how 

 to interpret with greater certainty the forms of the 

 valleys and the peaks into which this ancient range of 

 lunar mountains is broken up. 



It seems to me that we have some evidence of drainage 

 action upon the moon, in the curious dark patches on 

 the plains at the base of mountain slopes — see for 

 example the delta-like patch in the bay within the foot 

 hills between Archimedes and the lunar Apennines — a 

 dark form which is visible when the sun is at all 

 altitudes, showing that it cannot be due to shadows 

 cast by irregularities in the surface. In order to make 

 sure of what I refer to, I would ask the reader to compare 

 our plate with the Henry photographs (Knowledge, 

 December, 1890), and with the Lick photographs (Know- 

 ledge, October, 1889). There are also some dark spots, 

 which I believe to have a similar origin, on the other side 

 of the lunar Apennines, in a line between Archimedes and 

 Manilius, a crater about 25 miles in diameter, to the south 

 west of the Apennine range. These dark markings, as 

 well as the similar dark patches to the south-west of the 

 Palus Nebularum,"" are seen as dark when the sun is at all 

 altitudes ; and they are generally found near to the base 

 of mountain slopes in the equatorial regions of the moon. 

 It is hardly conceivable that these darker patches can be 

 due to a dift'erence in the nature of the surface rocks — 

 which crop out always towards the base of mountain 

 slopes — and the form of the patches seem to indicate a 

 flow of matter down a slope. They can hardly be lava 

 streams, for they are not associated with adjacent craters, 

 and the radiating narrower forms which have been usually 

 assumed to be lava flows from craters are generally 

 whiter than the surrounding s urface. 



* Tlie Palus Nobuliirum is tlie Miiallor ])Iain to the ca?t of 

 Manilius, aud to the south-west of the lunar Apennines. 



