[Footnote 7: Of Ammonites, _Mortoniceras rostratum_ and _Hoplites splendens_ may be mentioned: and of Pectens, _Neithea quinquecostata_ and _quadricostata_, _Syncyclonema orbicularis_, and _AEquipecten asper_.] Chapter VII THE CHALK As we have traced the world's history written in the rocks we have seen an old continent gradually submerged, a deepening sea flowing over this part of the earth's surface. Now we shall find evidence of the deepening of the sea to something like an ocean depth. We are coming to the great period of the Chalk, the time when the material was made which forms the undulating downs of the south-east of England, and of which the line of white cliffs consists, which with sundry breaks half encircles our shores, from Flamborough Head in Yorkshire, by Dover and the Isle of Wight, to Bere in Devon. Across the Channel white cliffs of chalk face those of England, and the chalk stretches inland into the Continent. Its extent was formerly greater still. Fragments of chalk and flint are preserved in Mull under basalt, an old lava flow, and flints from the chalk are found in more recent deposits (Boulder Clay) on the East of Scotland, pointing to a former great extension northward, which has been nearly all removed by denudation. In the Isle of Wight the chalk cliffs of Freshwater and the Culvers are the grandest features of the Island; while all the Island is dominated by the long lines of chalk downs running through it from east to west. Now what is the chalk? And how was it made? The microscope must tell us. It is found that this great mass of chalk is made up principally of tiny microscopic shells called Foraminifera, whole and in crushed fragments. There are plenty of foraminifera in the seas to-day; and we need not go far to find similar shells. On the shore near Shanklin you will often see streaks of what look like tiny bits of broken shell washed into depressions in the sand. These, however, often consist almost entirely of complete microscopic shells, some of them of great beauty. The creature that lives in one of these shells is only like a drop of formless jelly, and yet around itself it forms a complex shell of surprising beauty. The shells are pierced with a number of holes, hence their name (fr. Lat. _foramen_, a hole, and _ferre_, to bear). Through these holes the animal puts out a number of feelers like threads of jelly, and in these entangles particles of food, and draws them into itself. Now, do we anywhere to-day find these tiny shells in such masses as to build up rocks? We do. The sounding apparatus, with which we measure the depths of the sea, is so constructed as to bring up a specimen of the sea bottom. This has been used in the Atlantic, and it is found that the really deep sea bottom, too far out for rivers and currents to bring sand and mud from the land, is covered with a white mud or ooze. And the microscope shows this to be made up of an unnumerable multitude of the