DIASTROPHISM AND THE FORMATIVE PROCESSES 691 



plains. In the best photographs they are seen to have considerable 

 relief and to be crisscrossed in different directions by lines of debris 

 obviously shot from neighboring craters. They are thus at least 

 surficially covered with clastic debris. But granting that every- 

 thing which appears at this distance like lava really is lava, the 

 whole does not imply a liquefaction of the moon of any other order 

 than that signified by the great lava flows on the earth whose essen- 

 tial solidity is now beyond question. 



But let us look at the question of rapid infall quantitatively 

 and numerically. Let us assume that at the beginning of the 

 accretion process, one-third of the mass of the moon was already 

 in its core, while the remaining two-thirds had been gathered into 

 bolides five miles in diameter which were yet to fall in. The mass of 

 the moon is about 732X10'^ tons. There would then have been 

 244X10'^ tons in the moon-core and 488X10'^ tons in the bolides 

 yet to fall in. The mass of each of these bolides would have been 

 about 997 X 10^ tons, and their total number about 49 X 10^. Their 

 individual volumes would have been a little over sixty-five cubic 

 miles, while the volume of the moon-core would have been about 

 14X10^ cubic miles, and the radius of the core 708 miles. As the 

 radius of the full-grown moon is 1,080 miles, the core would have 

 had to grow radially 372 miles. 



Now the surface area of the moon-core would have been 6X10^ 

 square miles, while the disk of the five-mile bolides was a trifle less 

 than twenty square miles in area, so that there would have been over 

 300,000 disk-areas on the surface of the moon-core. It would 

 thus have required less than two hundred bolides to each disk- 

 area to complete the full growth of the moon. 



The liquid-forming impact theory now takes a critical form. 

 We have seen that the surface of the moon shows that the last 

 craters were not attended by general liquefaction or even a viscous 

 state of their immediate walls. The last falls, however, were 

 accelerated by nearly the full mass of the present moon, while the 

 first falls were accelerated by only one-third the mass of the moon. 

 The individual effects of the last infalls should, therefore, have 

 been greater than any that preceded. They should also have 

 inherited whatever benefits were transmissible from previous 



