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ideal conformity with the accretion hypothesis, if under that hypoth- 

 esis the process of accretion is conceived as dying away gradually by 

 a transition into a stage of dominant vulcanism, which in turn gradu- 

 ally passes into the present phase of dominant aqueous activity. On 

 the other hand, progressive investigation seems more than ever to give 

 negative results in the line of the discovery of "the original crust" 

 of the hypothetical molten stage, and the survival of the older hypoth- 

 esis will perhaps require the recognition of a dominant eruptive 

 stage similar to that postulated by the newer hypothesis, to which all 

 or most of the Archean rocks are to be referred. In the light of these 

 late Archean investigations, the difficulties of the old hypothesis seem 

 at least as great as those of the new, for the old hypothesis must 

 account for the non-appearance or scant appearance of "the original 

 crust," while the new must account for the non-appearance or scant 

 appearance of the supposed highly basic, magnesian, iron-bearing 

 meteoric matter. The new hypothesis has the advantage of having 

 theoretically postulated in advance what field studies are now bringing 

 into recognition in spite of prepossessions inherited from the older 

 view. 



Passing the problem of superficial constitution as not necessarily 

 serious, Fisher justly regards the increase of internal density and high 

 internal temperature as incontestable facts of radical importance, and 

 inquires how these facts may be accounted for on the meteoric theory. 

 He assumes the average density of the meteoric matter to be nearly 

 that of average surface rock, 2.75, and adds that "if this is too low, 

 the arguments based upon it will not be affected in any great degree." 

 Fisher feels tolerably certain that the law of internal density is fairly 

 represented by Laplace's law, which is that "the increase of the square 

 of the density varies as the increase of the pressure." In the case of 

 a slow growth by solid accretion, the internal density must be mainly 

 referred to compression. If, however, the specific gravity of the 

 original meteoric material be taken at some figure between 3.5 and 4, 

 as derived from known meteorites (Farrington's figure in 3.69), the 

 amount of compression is appreciably less than on the assumption of 

 2.75 made in the computations. Fisher finds that at a depth of 400 

 miles, where by Laplace's law the density should be 3.88 the compres- 

 sibility would be 1. 4021 X io~*5. "This may be looked upon as a small 

 compressibility, seeing that the compressibility of water similarly 

 measured is 4.78 X \o~^ or nearly forty times as great." The linear 



