26 EVOLUTION OF THE EARTH 



heading will now be discussed. It appears to the writer 

 that the chemical character of the igneous rocks, the limited 

 depth of density variations in the crust, the limited amount 

 of salt in the sea, the rotation periods of the moon and 

 planets, all point to a molten condition of the earth at the 

 completion of its growth. In the limited space available the 

 more technical aspects of the arguments must, however, be 

 omitted. The questions raised by this conclusion are : What 

 mode of growth would have favored a molten state and 

 how far did this precede the beginning of the geologic 

 record, as given by the oldest rocks exposed at the surface 

 of the globe? 



Up to this point the method of alternative hypothesis 

 has been pursued, and from the standpoint of scientific pro- 

 cedure it should be continued to the end. The limitations 

 of space in a single essay, however, forbid. This subject, 

 which for complete analysis should be developed in a volume, 

 must be compressed into a few pages. The judicial style 

 must often be abandoned for the declarative. Descriptions 

 of some things which no eye has ever seen will be given 

 graphically as though viewed by a witness. This change in 

 method necessitated by limitations of space is, however, 

 least objectionable in the closing parts of the subject, since 

 the foundation hypotheses have been already presented and 

 the argument leads from them toward the established facts 

 of the geologic record. 



Significance of the planetoids. The belt of asteroids, better 

 called planetoids, appears to have remained more nearly in 

 its original state than have other parts of the solar system. 

 The lack of aggregation into a planet may be due in part to 

 the absence of any dominating center. More than eight hun- 

 dred of these bodies have now been discovered and listed and 

 countless others must be so small that they will largely remain 

 unknown. The diameters range from a maximum of 485 



