DIASTROPHISM AND THE FORMATIVE PROCESSES 701 



Now, if these are the true lines of interpretation, the masses of 

 meteors and meteorites, and their methods of infall, throw a flood 

 of light on the sizes and the modes of infall of the planetesimals , for, 

 by this interpretation, they are bodies of like origin and like general 

 conditions. On a conservative estimate, there are 100,000,000 or 

 more minute meteorites, so small as to be wholly dissipated in the 

 upper air, for every one that is massive enough to remain a visible 

 body until it reaches the earth. Of the latter, none are known to 

 exceed a dozen feet in mean diameter. No meteorite has ever 

 been seen to produce melted soil or rock by its impact. When 

 collisions with bodies that have no atmosphere take place, local 

 melting probably results. The glassy bodies common in meteorites 

 may very likely be such products. But the retention of such 

 heterogeneous structures as are common in meteorites implies that 

 there has been no general liquefaction. In so far, therefore, as the 

 testimony of the aberrant factors bears on the size, rate of infall, 

 and liquefying power of their dynamic relatives, the planetesimals, 

 it supports the view that these are small, and in other respects it 

 is in close accord with the deductions hereinbefore drawn from 

 dynamical considerations. It is in intimate harmony with the 

 testimony of the normal factors of the system. 



Professor F. R. Moulton and Dr. W. D. MacMillan have been 

 kind enough to read the manuscript of this and the three previous 

 articles (X, XI, and XII), and to make valuable suggestions and 

 criticisms. They are not responsible, however, for the computa- 

 tions. These have been verified by Miss Daisy W. Heath. 



