THE ORIGIN OF THE EARTH. 37 



These planetesimals constitute one variety of meteoroidal bodies, 

 and it is to these that the brilliant August and September meteoritic 

 showers are assigned. It has not been quite demonstrated that they 

 are identical with the iron and stone meteorites above described, for 

 they do not generally reach the earth, and it is not positively known 

 that they have done so in any case, though one case of high probability 

 is known; but their essential identity is extremely probable. In the 

 fact that they have come to have individual orbits about the sun, 

 and that these orbits are roughly parallel to one another, and that 

 their velocities are of the same order, they do not represent the typical 

 meteoritic condition, as heretofore defined. They rather illustrate 

 the planetesimal phase of the meteoroidal condition. 



The foregoing hypothesis of the origin of meteorites makes them 

 but an incidental result of stellar and planetary action. Their genesis 

 is wholly a secondary matter, and furnishes no ground for regarding 

 meteorites as the parent material of great nebulae or of stellar systems. 

 The quantity of matter dispersed in this way is, by the terms of the 

 hypothesis, limited to an extremely small part of the total mass of 

 the system from which it is derived. It is therefore regarded rather 

 as an incidental result of trivial importance than as a primary con- 

 dition capable of generating great systems. This scattered matter 

 is presumed to be picked up bit by bit by all the larger bodies, as 

 is being done daily by the earth; and the maintenance of the supply 

 requires only the disruption of small bodies to an extent equal to the 

 trivial masses gathered in by the existing sims and planets. The 

 exceedingly small amount of meteoritic material picked up by the 

 earth is in harmony with this interpretation. 



The hypothetical nature of this discussion of meteorites will be 

 noted and due reserve in building other views upon it should be exer- 

 cised, but the suggestions made in it may have some value in rounding 

 out a consistent conception of the factors involved in the complex 

 problem of which earth-genesis is a part, and may be helpful in dis- 

 tinguishing between competent generating factors and merely inci- 

 dental by-products. 



In conclusion, it may be remarked that the meteoritic condition 

 seems most probably to be the product of incidental dispersion, and 

 to be the source of merely incidental accretion by existing bodies, 

 having neither great magnitude nor importance. It does not seem 



