672 W. M. DAVIS 



On the other side is the fear that theories may become our masters, 

 and that we may appeal to them as infahible, and tlius set ourselves 

 up as authorities. This is a most natural induction from the history 

 of our earlier progress, for we have repeatedly seen the sincere young 

 investigator grow into the impatient old autocrat; it is a bit of human 

 nature that we share with the rest of the world ; it is analogous to the 

 change of meaning in the word "tyrant," from a mere king to an 

 arbitrary despot. But there is another verbal analogy in the change 

 of the word "skeptic" from inquirer to doubter, and it is this analogy 

 that we are now following. We have learned to doubt because we 

 know we may be deceived ; we mistrust careless eyes as well as careless 

 thoughts, and insist that careful scrutiny be given to the work of both ; 

 we reduce the dangers of theorizing just as we reduce the errors of 

 observing, not by avoiding that indispensable means of investigation, 

 but by practicing it carefully, until we become experts in thinking as 

 well as in seeing ; and all this constitutes an important element in our 

 recent progress. 



In spite of what has already been gained by good theorizing, few 

 realize how largely earth science, apparently a matter of observation, 

 is really built up of inferences that go far beyond mere inductions. 

 Many of the inferences have gained a certification so good and so 

 familiar that in respect to verity they take rank with seen things, 

 and we are apt to forget their origin. The successive deposition of 

 bedded rocks, the organic origin of fossils, the original horizontality 

 and continuity of folded and eroded strata — these inferences are today 

 accepted as if they had never been doubted; but they all were once 

 doubted, and they had to make their way against opposition. What- 

 ever order of certainty they have now acquired, they are not facts 

 of observation, but facts of inference; and, like the great body of 

 earth science, these now well-accepted facts of past time have not 

 been determined by direct seeing, but by inference on the basis of 

 seeing. We may therefore justly claim great progress for earth 

 science, not only in the extent and accuracy of our observations, but 

 also in the extent and accuracy of our inferences. While there is 

 yet need of more conscious recognition and more thorough training, 

 especially in the deductive processes by which many problems may 

 be solved, we may still say that among the most significant steps we 



