The Second Period of the Earth
The Secondary Period marks the emergence of the dry land into importance greater than that of the sea.
TRIASSIC SYSTEM. The Triassic rocks chiefly consist of sandstones and hardened clays laid down in shallow sea basins. Land vegetation now first began to assume a modern type, with conifers and cycads. The seas were still richly peopled, and the land first gave a home to huge reptiles, or dinosaurs.
JURASSIC SYSTEM. This system is marked by a great variety of limestones, the product of dead sea creatures. It is essentially the age of reptiles. The ichthyosaurus disputed the seas with the plesiosaurus; the pterodactyl ruled the air; whilst on land, huge monsters like the brontosaur and diplodocus browsed on tropical vegetation. From these reptiles the birds were developing, whilst small marsupials, the oldest of the great mammalian race, skipped under the branches.
CRETACEOUS SYSTEM. This was the age of the great chalk deposits. The birds, now emerging from their reptilian ancestry, dominated its life, and the first modern plants appeared on the land.
The Third Period of the Earth
The Tertiary Period marks the true beginning of modern geological history, when the great outlines of geography were laid down, and the first representatives of modern plants and animals made their appearance.
EOCENE SYSTEM. The Eocene rocks are mainly limestones, with sandstone and hardened clays. We owe them to the sea and its organisms. Modern evergreen trees now first appeared. The mammals come to the front, with the tapir-like palæotherium and the first recognisable ancestor of the horse.
MIOCENE SYSTEM. The Miocene Age was a mountain-building period, when the great chain which runs from the Alps into Central Asia received its final uplift. Deciduous trees, like the beech and elm, now made their appearance. The giant mastodon and the formidable sabre-toothed tiger roamed the Miocene forest, and true apes—man’s first forerunners—mopped and mowed in the boughs.
PLIOCENE SYSTEM. The last of the Tertiary ages set the final stamp on the geological moulding of the earth’s crust. Its plants were transitional to the flora of modern Europe. Great herds of herbivora now appeared.