154 The American Geologist. September, i902 
If I have correctly stated the relations of geology to the 
other sciences, it follows as a corollfiry that those only can 
greatly advance the principles of geology who have a working- 
knowledge of two or more of the sciences upon which it is 
based. 
By a w^orking knowledge of a science I mean such a knowl- 
edge of its principles as makes them living truths. One must 
not only be able to comprehend the principles, but he must 
see them in relations to one another; must be able to apply 
them. It is not sufficient for a carpenter to be able to explain 
how the hammer, saw, plane, and chisel work ; he must be able 
to use them. He must be able to hit the nail on the head, to 
cut' straight, to plane smooth, to chisel true, and do all upon 
the same piece of timber so as to adapt it to a definite purpose 
in a building. Just so the geologist must be able to apply as 
topis the various principles of physics and chemistry and bi- 
ology and mineralog'x' to the piece of geology upon which he 
is engaged ; and thus shape his piece to its place in the great 
structure of geological science. This is what is meant by a 
working knowledge of the sciences basal to geology. 
It is not supposed that any one man has a comprehensive 
knowledg'e of all the basal sciences, or even a working know- 
ledge of their principles ; but such knowledge he must have of 
two or more of them if he hopes to advance the principles of ge- 
ology. He Avill be able to handle those branches of his subject 
with which he deals in proportion as he has a working knowl- 
edge of the basal sciences upon which his special branch is 
based, and will properly correlate this branch with the other 
branches of the great subject of geologv in proportion as his 
working knowledge of the basal sciences is extensive. 
For instance, to advance geological paleontology one must 
have a working knowledge of the principles of biology and of 
stratigraphy. To advance any of the lines of physical geology, 
one must have a working knowledge of the principles of phys- 
ics, and especially of elementary mechanics. To advance physio- 
graphy one must have a working knowledge of physics and che- 
mistry. To advance knowledge of the early history of the earth, 
one must not only have a working knowledge of physics and 
chemistry, but of astronomy. To advance petrology, one must 
have a working knowledge of physics, chemistry and miner- 
