SOME FUNDAMENTAL CONCEPTS OF EARTH HISTORY 161 
formitarianism, of which Lyell (1797-1875) rising to prominence 
a few years later, became the chief exponent. This school, carry- 
ing to its logical conclusion the statement of Hutton that “no 
powers are to be employed that are not natural to the globe, no 
action to be admitted of except those of which we know the 
principle, and no extraordinary events to be alleged in order to 
explain a common experience,” denied that there was any reason 
to suppose that geological agents have ever varied in their activ- 
ity, or in their potency to modify the features of the earth. 
While they served to break the shackles with which Catastro- 
phism had bound the science, the Uniformist doctrines have been 
displaced in large part by the principles of Evolution. The Evo- 
lutionist, although he holds on the one hand to the permanence 
of the laws and forces of Nature through all the earth’s history, 
also holds on the other hand that these forces have acted with 
varjdng intensity during different periods of that history. Thus 
there has been an interplay of laws and agents which has re- 
sulted in exceeding diversity of events and resultant forms. 
It may be said here that by the time Buff on published his 
Epoques de la Nature in 1778, Geology was becoming freed 
from the thrall of theological dogma; hence he felt at liberty to 
ascribe long periods of time to the development of the earth — 
that is, long as compared with the brief time previously alloted. 
He estimated from his experiments with cast-iron globes that the 
world began about 75,000 years ago and would come to an end 
93,000 years hence. While these figures seem small to the mod- 
ern geologist they represent a great advance beyond the limita- 
tions of earlier writers, and may be said to mark the beginning of 
an intelligent attempt to estimate the duration of geologic time. 
Undoubtedly the theory of earth origin which more than any 
other since .the beginning of the 19th century has influenced 
geologic thought, is that of La Place, known as the Laplacian or 
Nebular Hypothesis. Pierre Simon, Marquis de La Place, was 
born in 1749 of very poor farmer parents and died in 1827. He 
was one of the most brilliant of mathematicians and astrono- 
mers and through his studies of celestial mechanics was able to 
formulate more clearly than any other scholar of his own or 
previous time a theory of the origin of the solar system. This 
was published in 1796 as a footnote to his Exposition du systeme 
da mondc. According to this hypothesis the material of the solar 
11 
