It is no objection to these grand theories to urge that they do not explain the origin of the matter of the universe, either what it is or how it came to be where we now find it. We can only take one step at a time, and even if in these greater problems any further advance should be as yet denied us, it is still a great thing to have been able to take even one secure step into the vast and mysterious depths of the interstellar spaces. EVOLUTION OF THE EARTH’S CRUST Although Pythagoras (500 B. C.) believed that sea and land must often have changed places, and a few other observers at different epochs came to the same conclusion, yet, till quite recent times, the earth was generally supposed to have been always very much as it is now; people spoke of “the eternal hills”; and the great mountain ranges, the mighty ravines and precipices, as well as the deep seas and oceans, were believed to be the direct work of the Creator. It was only in the latter half of the eighteenth century that a few observers began to see the importance of studying the nature of the earth’s crust, so far as it could be reached in ravines, quarries, and mines; and one of the most earnest of these students, Dr. Hutton, of Edinburgh, after more than thirty years of travel and study, published his great work, _The Theory of the Earth_, which must be considered to be the starting-point of modern geology. He maintained that it was only by observing causes now in action that we can explain the phenomena presented by the stratified and igneous rocks; he showed that the former must have been laid down by water, and that the larger part of them, containing as they do marine shells and other fossils, must have been deposited on the sea-bottom. He showed how rain and rivers, frost and snow, wind and heat disintegrated the hardest rocks and would in time excavate the deepest valleys; while earthquakes, however small an elevation any one of them might produce, would in time raise the sea-bottom sufficiently high to form, when denuded, mountain ranges, plains, and valleys like those we now see everywhere upon the earth’s surface. He also showed that the most ancient stratified rocks, those that lie at the very base of the series, presented every indication of having been formed in exactly the same way as the most recent ones. Hence he stated a conclusion which excited a storm of opposition, in these words: “In the economy of the world I can find no traces of a beginning, no prospect of an end.” This was thought to imply a denial of creation, and was quite sufficient at that period to prevent the work of any man of science from being judged impartially.