394 FROM^ NEBULA TO NEBULA 



tude of possibly thirty feet, and will continue rising, 

 given the necessary supply of snow, until it telescopes 

 upon itself by its own weight. But to return to the moon : 



Naturally, the melted water that manages to seep 

 back into the basins must, while the sun is still high, im- 

 mediately undergo again the process of evaporation. Ow- 

 ing, however, to the frigidity of the planet's quiescent at- 

 mosphere, as well as to its own self -built prison walls, the 

 rising mist changes into snow before it escapes from the 

 caverns, in which condition it is, of course, undetectable 

 as vapor. Some of this snow doubtless spreads promis- 

 cuously over the planet's surface, but a major share of it 

 remains to restore and heighten the old walls. This pil- 

 ing-up process cannot go on indefinitely without even- 

 tually causing the peaks to telescope upon themselves 

 from time to time, partly on account of their own over- 

 gorged weight, and partly because of the undermining of 

 their bases by the periodical flooding of the bottoms. This 

 telescoping process gives us the key to the terraced effect 

 so generally observed on the inner sides of the crateral 

 ramparts and supplies the reason for the otherwise sur- 

 prising precipitousness of their faces. It also explains 

 why the mountains and ramparts automatically preserve 

 a maximum uniformity of height, and why the great ring- 

 walls present their characteristic squashy, convolute ap- 

 pearance. 



MOUNTAINS. Selenographers have in the past re- 

 garded as the most puzzling of all facts about the moon 

 "the presence of the most important mountain ranges in 

 the featureless districts termed seas, where the craters 

 are fewest." By my hypothesis, the mystery becomes a 

 mystery no longer. In the oceans, ivhen full, there could 

 not, of course, have been separate pools ; hence no craters. 

 But there were doubtless natural islands. These latter, 

 situated as they were in the very heart of the snow-pro- 

 ducing regions (these maria) accumulated the tremen- 

 dous loads, that now mark them to us as "mountains". 



The island of Cuba is 730 miles long, the lunar Ap- 

 pennines 450 miles. Imagine rapid changes of the sea- 



