scenes of the distant past, to which the science of geology introduces us, that I value it as a study, and wish earnestly to awaken you to its beauty and importance. It is because it is the science from which you will learn most easily a sound scientific habit of thought. I say most easily; and for these reasons. The most important facts of geology do not require, to discover them, any knowledge of mathematics or of chemical analysis; they may be studied in every bank, every grot, every quarry, every railway-cutting, by any one who has eyes and common-sense, and who chooses to copy the late illustrious Hugh Miller, who made himself a great geologist out of a poor stone-mason. Next, its most important theories are not, or need not be, wrapped up in obscure Latin and Greek terms. They may be expressed in the simplest English, because they are discovered by simple common-sense. And thus geology is (or ought to be), in popular parlance, the people's science—the science by studying which, the man ignorant of Latin, Greek, mathematics, scientific chemistry, can yet become—as far as his brain enables him—a truly scientific man.
But how shall we learn science by mere common-sense?
First, always try to explain the unknown by the known. If you meet something which you have not seen before, then think of the thing most like it which you have seen before; and try if that which you know explains the one will not explain the other also. Sometimes it will; sometimes it will not. But, if it will, no one has a right to ask you to try any other explanation.
Suppose, for instance, that you found a dead bird on the top of a cathedral-tower, and were asked how you thought it had got there. You would say, "Of course, it died up here." But if a friend said: "Not so; it dropped from a balloon, or from the clouds;" and told you the prettiest tale of how the bird came to so strange an end, you would answer: "No, no; I must reason from what I know. I know that birds haunt the cathedral-tower; I know that birds die; and therefore, let your story be as pretty as it may, my common-sense bids me take the simplest explanation, and say—it died here." In saying that, you would be talking scientifically. You would have made a fair and sufficient induction (as it is called) from the facts about birds' habits and birds' deaths which you knew.
But suppose that when you took the bird up you found that it was neither a jackdaw, nor a sparrow, nor a swallow, as you expected, but a humming-bird. Then you would be adrift again. The fact of it being a humming bird would be a new fact which you had not taken into account, and for which your old explanation was not sufficient: and you would have to try a new induction—to use your common-sense afresh—saying, "I have not to explain merely how a dead bird got here, but how a dead humming-bird."
And now, if your imaginative friend chimed in triumphantly with, "Do you not see that I was right after all? Do you not see that it
