Fig. 638.—Breakers on the coast of Cornwall.
It is the same by the seashore; the cliffs are wearing away, and the sea approaches; at other places the sea recedes from the land, as coral formation and embryo chalk cliffs are rising under the surface of the ocean. Lakes dry up, and the meadow or farm arises on the site, while other old spots are submerged. No rest, no change of idea, but ever changing in physical appearance, Nature goes on her wondrous way, working now as steadily, as harmoniously, and as surely as she did before time was, and as she will continue to do when time shall be no more!
In our investigations into Geology we cannot enter into many technical details. Our object in these pages is recreation; but we shall, even under these circumstances, find plenty to interest, and sufficient to lead any one who wishes to pursue the study for himself. We will endeavour so to put the features of the stones and rocks before him that they will be recognized by the passer by. We will try to show how the earth has been built up, and how the great and terrible changes through which our little globe has passed have been effected. In our own islands, Great Britain and Ireland, we shall find traces of all the materials likely to be useful to us in our quest, As has been well said, “Geology is the Physical Geography of the past.”
Constitution of the Earth.
Fig. 639.—Shells in chalk.
The descent from rocks to stones, from stones to gravel, from gravel to sand, is evident to everyone, so we need not insist upon the fact that sand is powdered rock, and that an aggregation of sand particles makes stones. We have heard in the Mineralogy section that there are certain “earths”—silica, alumina, lime, etc. Of these “earths,” the two former constitute the greater portion of the ROCKS. Lime, also, is very evident, and in limestones fossils or organic remains are abundant. Now we must entirely put away from our minds the old idea that the earth we live on was created at once, or as it appeared to the first human beings. Our planet was prepared for man by degrees during millions of years. We conclude that the earth was originally composed of certain elements, and we find the same elements in the sun. Therefore, supposing (as is supposed) that the earth came from the sun, we have all the material of the globe in a fused state. As the earth cooled, rocks were formed by pressure, and then water came, and now we can read “books in the running brooks, and sermons in stones” at our leisure.
Fig. 640.—The streamlet.
Perhaps as someone reads this he may be walking by the seashore kicking the pebbles or seated upon the sands, the grains of which are so very tiny. He will probably find sand, shingle, and gravel within reach, and perhaps the curious-looking “pudding stone.” Now what can we learn from these stones or sand grains or that curious bit of conglomerate? Perhaps the reader may be at Ramsgate or Margate or another place where the “white cliffs of Albion” glisten in the sun. Take up a piece of chalk and examine it. It is soft and soils your hands, and you will throw it away, perhaps—but don’t. Take it home and put it under the microscope or a good magnifying glass. What do you see?