h 



A CENTURY OF GEOLOGY. 547 



latest results of King and Kelvin give only twenty to thirty mil- 

 lions.* This the geologist declares is absurdly inadequate. He 

 can not work freely in so narrow a space — he has not elbow room. 



The subject is still discussed v6ry earnestly, but with little hope 

 of definite conclusion. One thing, however, must be remarked. 

 Both parties assume — the geologist tacitly, the physicist avowedly 

 — the nebular hypothesis of the origin of the solar system, and 

 therefore the early incandescent fluid condition of the earth as the 

 basis of all his reasonings. Now, while this is probably the most 

 reasonable view, it is not so certain that it can be made the basis 

 of complex mathematical calculation. There is a possible alterna- 

 tive theory — viz., the meteoric theory — which is coming more and 

 more into favor. According to this view, the planets may have 

 been formed by aggregation of meteoric swarms, and the heat of 

 the earth produced by the collision of the meteors in the act of 

 aggregation. According to the one view (the nebular), the heat 

 is all primal, and the earth has been only losing heat all the time. 

 According to the other, the aggregation and the heating are both 

 gradual, and may have continued even since the earth was inhab- 

 ited. According to the one, the spendthrift earth wasted nearly 

 all its energy before it became habitable or even a crust was 

 formed, and therefore the habitable period must be comparatively 

 short. According to the other, the cooling and the heating, the 

 expenditure and the income, were going on at the same time, and 

 therefore the process may have lasted much longer. 



The subject is much too complex to be discussed here. Suffice 

 it to say that on this latter view not only the age of the earth, but 

 many other fundamental problems of dynamical geology, would 

 have to be recalculated. The solution of these great questions 

 must also be left to the next century. In the meantime we sim- 

 ply draw attention to two very recent papers on the subject — viz., 

 that of Lord Kelvin, f and criticism of the same by Chamberlin.:}: 



. ANTIQUITY AND ORIGIN OF MAN. 



Even after the great antiquity of the earth and its origin and 

 development by a natural process were generally accepted, still 

 man was believed, even by the most competent geologists, to have 

 appeared only a few thousand years ago. The change from this 

 old view took place in the last half of the present century — viz., 

 about 1859 — and, coming almost simultaneously with the publica- 

 tion of Darwin's Origin of Species, prepared the scientific mind 



* Clarence King, American Journal of Science, pp. 45-51, 1893 ; Kelvin, Science, vol. 

 ix, p. 665, 1899. 



f Science, vol. ix, p. 665, 1899, % Ibid., p. 889, and vols, x and xi, 1899, 



