458 Geology as a Science and an Art. [August, 
on the principles of biology. Just as mineralogy and petro- 
logy give fadls concerning the minerals and rocks which are 
buried in the earth’s crust, which fadts may be interpreted 
on the principles of physical geography. 
Now, if we turn to Sir Charles Lyell’s master work on 
geology, first published more than fifty years ago, we shall 
find that its title runs as follows : “ Principles of Geology ; 
or, the Modern Changes of the Earth and its Inhabitants 
Considered as Illustrative of Geology” filth edition). In 
that book, therefore, and it is still and will long continue a 
standard work, we may say that the Science of Geology is, 
by implication, defined as the ancient physical and life 
history of the earth. The physical history is based on the 
application of our knowledge of those causes now in opera- 
tion, which modify the crust of the earth elaborated by the 
science of physical geography. The life history is based on 
the application of our knowledge of the fadls of animal and 
vegetable life elaborated by biology. This is the widest 
definition of geology. But from what I have said it will, I 
think, be seen that it is quite impossible to circumscribe a 
definite area of knowledge, and say, this is geology and 
nothing but geology. I have, therefore, prepared a table 
showing the manner in which geology is related to her sister 
sciences. 
Mathematics and Logic. 
Chemistry and Physics. 
Mineralogy and Petrology. Physical Geography. Biology. Palaeontology. 
(for fadts.) (for principles). (for principles.) (for facts.) 
v. „ ' ' » ' 
Physical. Geology, Paleontological. 
In that table are shown the two sub-divisions of geology, 
the one dependent on mineralogy and petrology for fadts and 
physical geography for principles, the other dependent on 
palaeontology for facfts and biology for principles. Chemistry 
and physics, which are placed above, deal with the isolated 
factors, of which the problems of the sciences below are the 
complex products ; while mathematics and logic, which are 
placed at the top, deal with the relations which may be 
established between the fadts or phenomena supplied by the 
underlying sciences. 
With the principles of all the branches of science, which 
are included in that table, the geologist should be acquainted. 
Of course I do not mean to say that he should attempt to 
keep abreast of all these branches of science. On the con- 
