CHAPTERS FROM THE PHYSICAL HISTORY OF THE EARTH. CHAPTER I. INTRODUCTORY. ADMIRABLY adapted as man's perceptions are to the ordinary conditions of life, they tell him little or nothing directly of the laws of nature, or the origin of matter familiar to his senses. Certain races of men, who have occupied the earth probably as long as any of their species, are still ignorant of, and indifferent to, the causes of natural phenomena presented daily to observation, but which have never become objects of inquiry or speculation to them. Before man has arrived at an age when he is capable of the simplest reasoning process, he has insensibly learned to accept, as a necessary part of his surroundings, the alternations of light and darkness, the changes of the seasons, and the more obvious results of the law of gravity; but is as little disposed to investigate these as to ask himself why he sees, hears, and feels. In the history of the growth of human intelligence, however, the starting-point of speculation has invariably been astronomy. No doubt the beauty and the apparent movement of the heavenly bodies would be calculated to arrest the attention more forcibly than any terrestrial phenomenon ; and the observations, however vague they might be, had a practical utility. They became measures of time and direction, sufficiently accurate for the purposes of primitive man; but, as civilization advanced among a people, the necessity arose for more exact standards, observations multiplied, and curiosity gave place to speculation. Ere long, mythology and astronomy joined hands, and priestcraft elaborated an empirical system of predictions and oracles from lunar phases, eclipses, and planetary movements. This was not science, although in this rude cradle it was born. Besides marking the times of religious festivals, the observations were of supreme importance in navigation—their only guides being the sun and stars to so adventurous a people as the Phonicians, whose voyages must frequently have taken them out of sight of land. Though the Chinese claim immense antiquity for their knowledge of astronomy, it does not appear certain that they turned their attention to any other branch of science. Even the Greeks, who had distanced all nations in metaphysics (and are yet unapproached in some departments of culture), remained content with a baseless theory of physics, embodied in the belief that the universe consisted of earth, air, fire, and water; and it was not until the world had lain under the dominion of Aristotle's philosophy for nearly twenty centuries, that any sound conceptions of the fundamental laws of nature began to be entertained. Still astronomy held its place, and discovery had no other domain. Physics and chemistry had not yet emerged from the regions of superstition and fancy; and science was without method, and research without principles, until the master mind of Bacon gathered up the broken threads of all the older philosophies, and wove them into a coherent system. Torricelli taught us how to measure the atmospheric ocean, and Lavoisier analyzed it, while Cavendish discovered the composition of water-starting-points for altogether new departures on the road of investigation. Now the importance of a knowledge of the constitution of our own planet was fully recognized, and observation and experiment rapidly cleared away the rubbish collected by astrologers and alchemists. Notwithstanding the marked advance in astronomy and chemistry, the interior of the earth remained almost unexplored, and its history a sealed book, until the beginning of the seventeenth century. Aristotle had remarked, in the "Meteorologics," that the distribution of sea and land was not permanent, and vaguely suggested periodic changes in their relations; but his observations applied to local and superficial conditions, leaving untouched the great mechanical agencies which have operated throughout all time. Strabo reasoned correctly-from the presence of marine shells at high levels, earthquakes, and volcanic eruptions on the movements beneath the surface; and, |