I will try now to give you some idea of the way in which the rocks come in their order, or the succession of formations as geologists call it. If we started to walk from Wales to London the rocks we should pass over would be—slate and flagstones in Wales, and going on towards London, limestone, old red sandstone, more limestones, coal beds, new red sandstone, oolite, greensand, chalk, and last London clay. We might not always find each of these near the surface, but they would be found to be the principal rocks on a line between Wales and London, the oldest being in Wales and the newest or most recent as we get nearer London. That word “oolite” which I used comes from two Greek words meaning “roe” and “stone,” because the rock is composed of little rounded grains of a chalky substance shaped like the hard roe of a fish, or like sago before it is cooked. If you look at the following table you will see how the principal rocks are placed one upon the other, beginning at the lowest or oldest at the bottom and going up to the newest at the top of the table, and on the right hand side I have written the names of the principal fossils which each kind of earth contains. TABLE OF THE SUCCESSION OF FORMATIONS. TERTIARY, or Upper Rocks Peat bogs and caves Fossil Man, with stone implements, River-mud and brickearth, &c., mammoth, gravels, and hippopotamus, rhinoceros, boulder clay (alluvium) Irish stag, cave lion, &c. Crag of Eastern Counties Numerous shell-fish, mastodon London clay, &c. Turtles, crocodiles, shell-fish SECONDARY, or Middle Rocks Cretaceous Chalk (with and without Foraminifera, &c., sponges, flints) corals, sea-urchins, shell-fish Greensand and gault (Belemnites, Ammonites, Wealden clay, &c. &c.), fishes Oolites Portland stone Kimmeridge clay Coral rag Immense reptiles, the Ichthyosaurus, Oxford clay Plesiosaurus, Cornbrash and forest Megalosaurus, Pterodactyl, marble &c. Great oolite Fullers’ earth Animals allied to the opossum Lower oolite and kangaroo Lias clay and limestone Cycads and other plants New red marl and sandstone PRIMARY, or Lower Rocks Coal Ferns, club-mosses, a few Millstone grit firs, calamites, &c., in Mountain limestone great abundance Old red sandstone Numerous corals, shell-fish, Silurian limestones and trilobites, fishes, &c. slates Cambrian slates The Laurentian rocks contain Laurentian rocks the oldest known fossil, the Eozöon (or “life-dawn animal”) IGNEOUS, or Volcanic Rocks