From the investigations of geologists we have learned the fact that the horse is descended from ancestors which existed in long-past ages of the world's history, and which were very different in many respects from the animal so familiar to us. Probably it will be very generally thought that it is late in the day to attempt to question, or even to defend, the teachings of geology, and the kindred subject of paleontology, or the science of extinct animal and vegetable life. At one period, however, not so remote as to be out of the recollection of many of the readers of to-day, the suggestion that the remains of animals and plants were to be found in certain "petrifactions", dug up from the depths of the earth, was met by opposition which was as violent as it was honest and ignorant.
Education has made rapid strides in all directions since the day of merely unreasoned opposition to the advance of science; and it may perhaps be said that the majority has changed its front, and is now either in favour of investigation and receptive to its results, or at least accepts them without any great effort, possibly it may be with some degree of indifference, but in any case no longer opposes them. On either assumption it will be no more than fair to the reader who may not be a scientist, and it will at the same time be inoffensive to the geologist and palaeontologist, for whom the remarks are not intended, if we state in a few concise sentences the broad principles on which those experts base their arguments and conclusions.
In the first place it may be observed that it is now well known that rocks of different sorts constitute what is called the crust of the earth-that is, the superficial portion accessible to human observation - and what is more significant, that these rocks are not for the most part Leaped together in disregard of order, but are arranged in a certain succession of beds, or strata, from below upwards. The lowest rocks bear evident signs of the action of heat, and not being arranged in layers or strata, are distinguished as unstratified rocks, being also more or less crystalline The higher rocks, above those more ancient igneous rocks, whether hard or soft, were originally deposited from water in the form of sediment, and hence are called sedimentary or aqueous rocks. These are stratified, and in them the remains of animals and plants are found more or less abundantly, such remains being absent from the igneous rocks. The name fossils is now familiar to everyone as applied to the remains of animals and plants found in rocks, and this term also includes markings, such as footprints and casts or impressions left on originally soft clay on which the object has rested or in which it has been enclosed.
To the discoveries of the geologist the naturalist applies the same mental processes which he uses in everyday life. He can see impressions which have been left on the sea-shore, footmarks of men and beasts on the sands, and, observing the marks, he realizes at once the existence of the different creatures that made. them. A skull or a leg-bone dug up from a stone quarry or gravel-pit may attract his notice, and by the application of his knowledge of anatomy he can decide whether the part once belonged to a man or to an ox, a pig or a horse, and with added special knowledge he will go beyond this and define the formation from which it came, and form some idea of the period which has elapsed since it was deposited. In like manner the geologist sees how river banks and seawalls are washed away year by year, and in other places how hollows are gradually filled by sedimentary deposits, which are left to harden into rocks, and by the exercise of his ordinary intelligence he comprehends how the strata in the earth's crust have been formed in succession by similarly slow and often-interrupted actions going on through long ages. It is of no avail to tell the palaeontologist that the impressions of animals' feet, and the marks of shells and skeletons of birds and beasts and fishes, are not what they seem to him, but only "petrifactions", or "fossils", curious enough and highly interesting indeed, but in no way connected with living creatures of a former period, when all the while his senses of sight and touch inform him to the contrary. He can compare the fossil bone of many thousand years ago with the corresponding bones of the animals of to-day and mark the close relation between them. In fact, he is aware that often, in comparing the later fossil remains with specimens of similar parts of recent origin which have been buried close to the latest fossils, he finds a difficulty in distinguishing between them. In short, the scientist observes and reasons exactly as other people do. Of his facts he is as sure as any enquirer into everyday common things can be of his, and like him he exercises his intellect and imagination in drawing conclusions from the facts which come under his observation.
It is true that some difference may exist between the mental processes of the expert and those of the unscientific observer, but it is only one of degree. The scientist is a trained, and therefore a keen investigator, and his imagination is active as well as critical. Small matters which an ordinary looker-on may pass by, the expert seizes and does not allow to escape until he has exhausted their teaching. The method of Zadig is the one which he, perhaps unconsciously, adopts in all his enquiries. What that method is most people know, but as it may have been known and forgotten, it may be well to follow Huxley's example in his lectures on evolution and quote the short story of the sage entire.
According to Voltaire, Zadig, whose country, indeed whose existence, is problematical, dwelt on the banks of the Euphrates, and occupied his lonely life in the close study of nature. Thus by degrees he acquired a marvellously keen power of observation and profound sagacity, of which the following example may be given: -