CHAPTER XII. GEOLOGICAL CHRONOLOGY--PRINCIPLES OF THE SYSTEM EXPLAINED AND DEVELOPED. Significance of Fossil Remains--Science of Palæontology--Classification of existing Animal Life--Fossil Remains are found to fit in with this Classification--Succession of Organic Life--Time in Geology not measured by Years and Centuries--Successive Periods marked by Successive Forms of Life--The Geologist aims at arranging these Periods in Chronological Order--Position of the various Groups of Strata not sufficient for this purpose--It is accomplished chiefly through the aid of Fossil Remains--Mode of proceeding practically explained--Chronological Table, 198 CHAPTER XIII. GEOLOGICAL CHRONOLOGY--REMARKS ON THE SUCCESSION OF ORGANIC LIFE. Summary of the History of Stratified Rocks--Striking Characteristics of certain Formations--Human Remains found only in superficial Deposits--Gradual Transition from the Organic Life of one Period to that of the next--Evidence in favor of this Opinion--Advance from Lower to Higher Types of Organic Life as we ascend from the Older to the more Recent Formations --Economic Value of Geological Chronology--Illustration--Search for Coal--the Practical Man at Fault--the Geologist comes to his aid, and saves him from useless Expense, 217 CHAPTER XIV. SUBTERRANEAN HEAT--ITS EXISTENCE DEMONSTRATED BY FACTS. Theory of Stratified Rocks supposes Disturbances of the Earth’s Crust--These Disturbances ascribed by Geologists to the Action of subterranean Heat--The Existence of Subterranean Heat, and its Power to move the Crust of the Earth, proved by direct Evidence--Supposed Igneous Origin of our Globe--Remarkable Increase of Temperature as we descend into the Earth’s Crust--Hot Springs--Artesian Wells--Steam issuing from Crevices in the Earth--The Geysers of Iceland--A Glimpse of the subterranean Fires--Mount Vesuvius in 1779--Vast Extent of Volcanic Action--Existence of subterranean Heat an established fact, 233 CHAPTER XV. SUBTERRANEAN HEAT--ITS POWERS ILLUSTRATED BY VOLCANOS. Effects of subterranean Heat in the present Age of the World--Vast Accumulations of solid Matter from the Eruptions of Volcanos--Buried Cities of Pompeii and Herculaneum--Curious Relics of Roman Life--Monte Nuovo--Eruption of Jorullo in the Province of Mexico--Sumbawa in the Indian Archipelago--Volcanos in Iceland--Mountain Mass of Etna the Product of Volcanic Eruptions--Volcanic Islands--In the Atlantic--in the Mediterranean--Santorin in the Grecian Archipelago, 244 CHAPTER XVI. SUBTERRANEAN HEAT--ITS POWERS ILLUSTRATED BY EARTHQUAKES.