122 FROM NEBULA TO NEBULA 



By applying the principles thus far gained the 

 reader should find little difficulty, by the exercise of 

 his scientific imagination, in accounting for at least 

 the simpler forms of the moon's asperities. A "sugar- 

 loaf" mountain, for instance, is a snow-bedecked soli- 

 tary island in the midst of a former sea; the Appen- 

 nines, a very longitudinal island, similarly located, and 

 upholding a similar burden, and so on. Hut while the 

 mountains are thus growing, the sea level is corre- 

 spondingly falling, thereby bringing to light the higher 

 and then less high prominences on the ocean bottoms, 

 each new emerging island fnrnishinf/ a fresh base for 

 the flakes to build upon; the whole process endinff in a 

 multitude of squat formations exactly correspondmg 

 to their taller brethren on the mainland. 



BUT THE CRUCIAL TEST OF MY THEORY IS ITS COM- 

 PLETE AND SATISFYING ABILITY TO HE-CREATE THE C RA- 

 TER AL FORMS, BIG AND LITTLE, OF EVERY CAPRICIOUS 

 VARIETY. 



In elucidating a general principle it is usually 

 much simpler and more satisfactory to choose a con- 

 crete example. Let us picture to ourselves, therefore, 

 a circular cistern twelve feet in depth and a hundred 

 feet in diameter. Instead of the walls being vertical, 

 however, let us imagine them sloping downward toward 

 the center of the bottom, but so as to leave a circular 

 flat space, say 2r> feet in diameter. Now. for the sake 

 of easy reference conceive of this slope as cut into four 

 steps, each a yard in height. We shall then have a 

 structure 4 resembling the pit of a Roman amphitheater. 

 Again, let us picture standing on the bottom a num- 

 ber of granite blocks respectively 2, 4, 8 and 10 feet 

 in height, to represent natural protuberances. Let us 

 now fill the cistern to the brim with water, thus sub- 

 merging all thr blocks, and start the natural process 

 of evaporation and snowing, limiting at the same time 



