472 THE HORSES POSITION IX THE ANIMAL WORLD 



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 crystallina. 

 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 abun- 

 dantly, 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 appli- 

 cation 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 sea- 

 walls 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 l)y 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 

 jjarts 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 



