THE CRUST OF THE EARTH. SKETCH OF GEOLOGY (Continued). Ion. Please, dear papa, you have nade a mistake; at least, we suppose that you did, because, in the little drawing at the end of the last lesson, you have called the second set of rocks the Secondary Rocks. P. It should have been Transition. I cannot tell, Willie, how the mistake happened. There are a few mistakes in the other parts, which I must leave you to correct yourselves. You will be sure to have noticed them, if you have read the lessons carefully. The rocks I spoke of in the last lesson were Ion. The Primary Rocks, and the Transition Rocks. P. To-day we will begin where we left off last time, at the Transition Rocks. I said that the time when these rocks were formed, was the beginning of a great period called the fifth day. There was broad daylight then, and the bright sun shone on a surface of water and land. But how different was its appearance then and now! Look at your Map of the World now, and you will mark five great pieces of land-Europe, Asia, Africa, America, and Australia. But then, the greater part of Europe, Asia, and the northern lands were covered with water, and very large islands were beginning to rise. L. What, move up, papa? Ion. Islands are not alive, papa. I have heard of the sun rising, but P. Ah, this is quite a different thing. This rising is caused by the action of the heat. When you have had baked custard for dinner, perhaps you may have sometimes noticed a few little brown swellings on the surface. W. I have, papa; they are like blisters. I have broken them with my spoon. P. Well, the matter or substance of this globe was then just as easily acted upon by the heat as the enstard. (Indeed it is so now.) We shall see how the heat under the earth has caused great swellings on its surface. There are some smooth gentle risings on the surface. These are in the parts where the action of the heat was not very strong, or where perhaps the strata of aqueous rocks were very tough, so that they would bend, and not burst. But, in other parts, the strata of rocks have not been strong enough to resist the fire. Then, the melted matter beneath has burst through, boiling up to a great height. This matter, as it cooled, formed very great swellings, which in time became quite cold, and were covered with earth. Do you know what these " very great swellings" are called, now? Ion. Mountains, I suppose. W. So do I. But when these great mountains were in the sea, I suppose that if they were tall enough to get their heads above water, they formed islands. P. That is right, Willie. The islands in the sea are only the tops of mountains and rocks under water. But let us proceed with the history of the fifth day; we have a long, long period before us. The Primary and Transition rocks had been formed. All Europe and the northern half of the globe, with the exception of a few very large islands, was, I said, covered with water, and the sun shone on the quiet earth and sea. Still quiet! not a sound, but the "rumbling" sometimes caused by the fire beneath, or the gentle ripples or angry roar of the water above. But sometimes there was no wind about, and the sea was lazy; then it was very quiet. Yet I told you there was life. The vegetables-the branched, the soft-bodied, the jointed, and even back-boned animals-the fisheswere there; they were all living and growing, but none of them uttered a sound. These "moving creatures, which had life," moved silently in the sea. As yet there were no animals on the land. And there was good reason for this too-no animals could have lived there. You have heard of the gas carbon. Your mamma told you, Ion, how the air carried away the carbon from the blood in your lungs, but imagine the air to be full of carbon! Ion. I suppose that when we breathed, we should have too much carbon in our lungs, and be suffocated. P. You certainly would, Ion. And at the beginning of the fifth day, the air was full of carbon. That is why there were no land animals or men. The place was not ready for them. L. Then that carbon would have to be cleared away first, and the air must be made pure. I wonder what God did with the carbon. . Where did he put it? P. It must have been put away somewhere, for none of it was lost. God never loses anything that He has made, nor wastes it, not even the most minute particle of carbon. The fact is, it was intended to be used up, and we are using it now. Just poke the fire, Ion. There it there it burns and blazes with a merry flame. L. What do you mean, papa? Are you talking about the coals? Ah, the French word for coal is charbon. Is coal carbon? W. And you said, papa, that the carbon was a gas. How can it be in coal? P. Ah, there is a mystery! Have patience, and listen. First, we will inquire, how was the carbon in the air cleared away? There were millions of beautiful insects at work in the sea, just at this time; they were busy using up the lime they found in the water, and making it into rocks, which we call coral rocks. There were also millions of shell-fish, whose shells were made of lime. As ages passed on, and these shell-fish were continually dying, their shells and the works of the coral insect being pressed down by the water, made a thick stratum of rock, which was nearly all lime. W. What is that stratum called, papa? P. It is called Limestone Rock. Do you remember my lesson on lime-whether I said anything to you about carbonic acid gas? Ion. Yes, papa. You said that the lime has an affinity for it-absorbs it, forming carbonates of lime. P. That is true. Then think how much carbon this great stratum of limestone must have absorbed! For it was a very thick stratum. And again, it was spread over a very large surface. It was even found on the high mountains, so that it is called Mountain Limestone. W. Then that was one way in which the carbon was cleared away is! the old carbon gas that was in-by making limestone to absorb the air ten thousands of years ago it was there any other way? This is called a Fern Plant. If we could have been in the world to see the islands and broad lands formed by the layer of mountain limestone, we should have seen these fine plants growing on the surface in immense jungles. The lands were also clothed with thick forests of other mighty trees, perhaps even larger than the great palm and sago trees which grow now in hot countries. All these plants and trees grow for many years by feeding on the carbon which they were "clearing away" from the atmosphere. W. How very plump and woody they must have grown! P. Yes, for they had the land all to themselves. There was still a solemn silence on the earth-intense silence. No animals lived in those fine trees. No bird sang to them. No insect hummed. No sound broke the dreary solitude of the deep, dark, shady forests. Ion. But I suppose that some animals were made as soon as the carbon was absorbed from the air? P. No. These fern plants and other trees had no flowers on them; where there are no flowers on a plant, there will be no fruits -and when there are no fruits, then the Animals L. They would have died if they had been made. They could not live on the leaves, I suppose. Then what would become of these great forests, after all? They were of no use, not even to chop up for fire-wood. P. Yes, indeed. Let me tell you again. God uses up everything, nothing is wasted. These old trees! He has kept them ever since for men to "chop up for firewood." Yes! He put them away for us ten thousands of years before we were born. He knew that on "the sixth day," He should | the beautiful forest trees!-They make man. And he did not are lost beneath the waves, and forget to think even of such little pressed down by an enormous people as Lucy, Willie, Ion, and weight of sand, grit, stones, earth, Ada, who, as well as the rest of and mud. mankind, like to sit by a nice fire. So-He made it into Coal for us. Should we not love Him now very much, whenever we look at the coals? What a kind Father! Think again of his making coal for us before we were made. L. And making fresh air for us at the same time!-But do, papa, tell us how it was done. P. Yes, so I will. But it is a terrible tale. Can you think of this Island of Britain? W. Yes. We are thinking about it-I am. P. Well, then,- —on this Island of Britain the stately ferns and forest trees, in their silent grandeur, grew up fresh and green. When, lo! God sent the waters upon them. The fire beneath began to move and shake the earth again-to rock it to and fro. The trembling earth quaked, and the earthquake shook the sea, as well as the land. Think, for a moment, that you can see it. Now, God moves the sea. Listen! Ah, listen, and look, as the rising and foaming sea roars, and the mad waves dash on. The rivers, too--Look at them! As the mountains shake, they pour down in torrents, flooding the land-rising even to the tops of the trees. Down they rush to flee away from the troubled hills, tearing down the single trees, and rocks, and earth. Then, as God moves the fire beneath once more, the forest again rocks to and fro; and as the land seems to sink the angry sea rising to a great height, sweeps onwards the sands from the shore-and, ah! Yes. - Turn away your eyes! -The forest is gone.-It is "put away," and all is silent as before. The island is sunk; the trees are buried alive. Over all are the waves, which are quiet again; and, like waves which are half-ashamed of themselves, they just splash backwards and forwards in an idle, indifferent mood. The forests in time were changed into coal-for they were pressed down and jammed together by the weight above. This pressure caused heat-so that the pressure from above and the heat from beneath caused them to burnbut not flame. W. I suppose that they could not make flames; there was no room for them. P. Or rather say, there was no air.-The trees, therefore, did not lose their carbon, but changed into charcoal. This charcoal became gradually harder, until it formed the substance we call Coal. And now-what changes there are! In the very place where, if a man could have stood thousands of years ago, he would have said, "Glorious forest!" he now says, "Durham Coal field." W. And "The present cash price, 23s. per ton." P. This is a very long lesson. I hope that the Printer will print it all. Let us remember what we have learned. We have begun to talk of the Secondary Rocks-and have heard of THE MOUNTAIN LIMESTONE, and PERSPECTIVE. P. Let us recapitulate a little. What do you call a figure with three sides? L. A triangle. P. Tell me the four-sided figures you have heard of. L. The rhomb-the rectanglethe parallelogram-and the trapezium. P. Let me hear you describe a square? What is a rhomb? What is a rectangle? What do you call the line drawn through a picture to show which objects are on a level with the eye? L. The horizontal line. P. What do you call the point in the horizontal line opposite to the point of station? Ion. The point of sight. P. What do you call the point opposite to the point of sight, the place where you stand to look at the picture? Ion. The point of station. P. What is the use of the point of sight? Ion. When we make a side-view of any objects, and draw the horizontal lines of those objects, they must all slant. And they must slant in such a way that they would meet at that point if they were long enough. P. In what direction would they slant? W. I can tell you, papa. In different directions. The lines above the point of sight must incline down to it, and those below the point of sight must incline upwards-just as you may see in An accurate definition of each figure should be given by the reader. this side view of a ladder which Ion and I have drawn. If the ladder were exactly in front of us, all the rails would be drawn with horizontal lines,-and, now you see, papa, that some of the lines slant upwards and some down, as I told you. P. But one of the lines is quite horizontal. W. Yes. That is because it is exactly on a level with the eye,-so it falls on the horizontal line, and it must be horizontal. P. I can understand. If you please, here is one more question. I said that when you are drawing objects in perspective, the lines of some of them must incline to the point of sight; while in others the |