372 FROM NEBULA TO NEBULA 



trast which the moon thus presents to the earth, where mountain 

 ranges are the rule and craters like the lunar ones are decidedly 

 exceptional. Another conspicuous but inexplicable fact is that 

 the most important ranges upon the moon occur in the northern 

 half of the visible hemisphere where the craters are fewest and 

 the comparatively featureless districts termed seas are found. The 

 finest range is that named after our Appennines. It extends for 

 about 450 miles and has been estimated to contain 3000 peaks, one 

 of which Mount Huyghens attains the altitude of 18,000 feet. 

 * * * Another considerable range is the Alps situated between 

 the Caucasus and the crater Plato. It contains 700 peaked moun- 

 tains and is remarkable for its immense valley 180 miles long 

 and about 5 broad that cuts it with seeming artificial straightness 

 and that, were it not for the flatness of its bottom, might set 

 one speculating upon the probability of some extraneous body 

 having rushed by the moon at an enormous velocity, gouging the 

 surface tangentially at this point and cutting a channel through 

 the impeding mass of mountains. * * * At first thought it might 

 appear that the great mountain ranges were produced by bodily 

 upthrustings of the crust of the moon by some sub-surface con- 

 vulsions. But such an explanation could hardly hold in relation 

 to the isolated peaks, for it is difficult, if not impossible, to con- 

 ceive that these abrupt mountains, almost resembling a sugarloaf 

 in steepness, could have been protruded en masse through a 

 smooth region of the crust. * * * We believe they may be re- 

 garded as true mountains of exudation, produced by the com- 

 paratively gentle oozing of lava from a small orifice and its sol- 

 idification around it, the vent, however, remaining open and the 

 summit or discharging orifice continually rising with the growth 

 of the mountains. 



LUNAR SURFACE CHANGES 



The reader, I trust, recognizes the impossibility of 

 discussing in detail the multitudinous data on this sub- 

 ject of lunar changes in the short space of a single chap- 

 ter, and I shall therefore compress what must here be 

 said in the narrowest possible space. To give him, there- 

 fore, the most information on this fascinating subject in 

 the fewest and clearest of words,! shall quote, rather 

 disconnectedly, I regret, from Professor Pickering's in- 

 valuable contributions as they have recently appeared in 

 Popular Astronomy (Nos. 219, 223, 237, 238) to which 

 the interested reader is earnestly referred : 



