The physical record is also very old. Its story is carved in a script that is often hardly legible, and set forth in symbols that are not easy to decipher. The testimony of the rocks embodies results of creation, but does not present the actual operations. Effects suggest processes, but do not disclose their precise measure, manner, and origination. You may dissect a great painting into its ultimate lines and elements, and from the canvas peel off the successive layers of colour, and duly record their number and order; but when you have done you have not even touched the essential secret of its creation. In determining the first origin of things the limitation of science is absolute, and even in tracing the subsequent development there is room for error, ignorance, and diversity of explanation. Of certainties in scientific theory there are few. For the most part, all that can be attained is probability, especially in speculative matters, such as estimates of time, explanations of formation, and theories of causation. As in exegesis, so in geology, all hypotheses ought to be counted merely tentative, maintained with modesty, and held open at every point to revision and reconstruction. The necessity of caution and reserve needs no enforcing for any one who knows the variety and inconsistency of the phases through which speculative geology has passed in our own generation. In this destiny of transitoriness it does but share the lot of all scientific theory. Professor Huxley was once cruel enough to call attention to the fact that "extinguished theologians lie about the cradle of every science, as the strangled snakes beside that of Hercules." The statement is a graphic, if somewhat ferocious, reminder of a melancholy fact, and the fate of these trespassing divines should warn their successors—as the Professor means it should—not to stray out of their proper pastures. But has it fared very differently with the mighty men of science who have essayed to solve the high problems of existence and to make all mysteries plain? Take up a history of philosophy, turn over its pages, study its dreary epitomes of defunct theories, and as you survey the long array of skeletons tell me, are you not reminded of the prophet who found himself "set down in the midst of the valley which was full of dry bones: and, behold, there were very many in the open valley; and, lo, they were very dry"?