Stuck all through this chalk, like plums in a cake, are hard flints or pebbles, and these can be cut and polished into very pretty jewelry. The Chalk age was one of great and violent changes. Once more the continents began to sink. The earth-crust could not uphold the mighty weight of deposit upon it. The shrinking and cooling core caused the settling of vast stretches of land, and the continents were depressed lower than they had been since the time of the first continent. Down, down went the land, and over it the waters flowed, and where hills and forests had been, creatures of the deepest depths of ocean played. Europe probably settled lower than America. Once more the globe was like a vast ocean, above which rose what had been high ranges of mountains, now forming long islands or reefs. Of these surrounding ridges might have been noted the hills of Great Britain, the Scandinavian Mountains, and the Ural range. In the Western hemisphere the hills of the St. Lawrence and the Appalachian Mountains rose over the water, and here and there a peak of the Rockies or the Andes. Why did the little hills of Britain rise up when the great Alps and the Himalayas were not to be seen? Britain itself did not sink so low at that time, and the Alps and the Himalayas were not yet born. They rose at a later day. The seas ebbed and flowed and deposited their chalk sediment over a drowned globe for a very long time. Then once more the earth crumpled, and amid earthquakes and volcanoes the Chalk age perished, the Rocky Mountains, Alps, and Himalayas were crowded and tilted up to be the great mountain-ranges of the world, and the last building-time of the earth had come. FOOTNOTES: [13] Marl is also used with sand in making Portland cement. LESSON V. THE PALM AND THE MAN. “So careful of the type she seems, So careless of the single life. ‘So careful of the type?’ but no, From scarped cliff and quarried stone She cries, ‘A thousand types are gone, I care for nothing, all shall go!’” --TENNYSON, _In Memoriam_. [Illustration: READY FOR MAN.] What have we thus far found to be the processes of earth-building? First, rocky crust uplifted into mountain ridges. Then deposit of sediment by the waters until islands and continents capable of maintaining animal and vegetable life are formed. Ages of increase and successive growth follow; then sinking of the earth-crust, accompanied by earthquakes and volcanoes; after this, fresh upheaval. With these surface changes come changes in the plant and animal life, especially in the former; for plants seem not to have the happy faculty of animals in accommodating themselves to new conditions. With the changing ages some animals entirely disappear, and are known to us only by their fossil remains. Others are modified and fitted to their new home.