The Students Elements of Geology | Page 4

which the rapid advance of the science had given rise, and when I proposed to bring out a new edition of the "Elements" I was strongly urged by my friends not to repeat these theoretical discussions, but to confine myself in the new treatise to those parts of the "Elements" which were most indispensable to a beginner. This was to revert, to a certain extent, to the original plan of the first edition; but I found, after omitting a great number of subjects, that the necessity of bringing up to the day those which remained, and adverting, however briefly, to new discoveries, made it most difficult to confine the proposed abridgment within moderate limits. Some chapters had to be entirely recast, some additional illustrations to be introduced, and figures of some organic remains to be replaced by new ones from specimens more perfect than those which had been at my command on former occasions. By these changes the work assumed a form so different from the sixth edition of the "Elements," that I resolved to give it a new title and call it the "Student's Elements of Geology."
In executing this task I have found it very difficult to meet the requirements of those who are entirely ignorant of the science. It is only the adept who has already overcome the first steps as an observer, and is familiar with many of the technical terms, who can profit by a brief and concise manual. Beginners wish for a short and cheap book in which they may find a full explanation of the leading facts and principles of Geology. Their wants, I fear, somewhat resemble those of the old woman in New England, who asked a bookseller to supply her with "the cheapest Bible in the largest possible print."
But notwithstanding the difficulty of reconciling brevity with the copiousness of illustration demanded by those who have not yet mastered the rudiments of the science, I have endeavoured to abridge the work in the manner above hinted at, so as to place it within the reach of many to whom it was before inaccessible.
CHARLES LYELL.
73 Harley Street, London, December, 1870.
CONTENTS.



CHAPTER I.
ON THE DIFFERENT CLASSES OF ROCKS.
Geology defined. Successive Formation of the Earth's Crust. Classification of Rocks according to their Origin and Age. Aqueous Rocks. Their Stratification and imbedded Fossils. Volcanic Rocks, with and without Cones and Craters. Plutonic Rocks, and their Relation to the Volcanic. Metamorphic Rocks, and their probable Origin. The term Primitive, why erroneously applied to the Crystalline Formations. Leading Division of the Work.



CHAPTER II.
AQUEOUS ROCKS-- THEIR COMPOSITION AND FORMS OF STRATIFICATION.
Mineral Composition of Strata. Siliceous Rocks. Argillaceous. Calcareous. Gypsum. Forms of Stratification. Original Horizontality. Thinning out. Diagonal Arrangement. Ripple-mark.



CHAPTER III.
ARRANGEMENT OF FOSSILS IN STRATA-- FRESH-WATER AND MARINE.
Successive Deposition indicated by Fossils. Limestones formed of Corals and Shells. Proofs of gradual Increase of Strata derived from Fossils. Serpula attached to Spatangus. Wood bored by Teredina. Tripoli formed of Infusoria. Chalk derived principally from Organic Bodies. Distinction of Fresh-water from Marine Formations. Genera of Fresh-water and Land Shells. Rules for recognising Marine Testacea. Gyrogonite and Chara. Fresh-water Fishes. Alternation of Marine and Fresh-water Deposits. Lym-Fiord.



CHAPTER IV.
CONSOLIDATION OF STRATA AND PETRIFACTION OF FOSSILS.
Chemical and Mechanical Deposits. Cementing together of Particles. Hardening by Exposure to Air. Concretionary Nodules. Consolidating Effects of Pressure. Mineralization of Organic Remains. Impressions and Casts: how formed. Fossil Wood. Goppert's Experiments. Precipitation of Stony Matter most rapid where Putrefaction is going on. Sources of Lime and Silex in Solution.



CHAPTER V.
ELEVATION OF STRATA ABOVE THE SEA.-- HORIZONTAL AND INCLINED STRATIFICATION.
Why the Position of Marine Strata, above the Level of the Sea, should be referred to the rising up of the Land, not to the going down of the Sea. Strata of Deep-sea and Shallow-water Origin alternate. Also Marine and Fresh-water Beds and old Land Surfaces. Vertical, inclined, and folded Strata. Anticlinal and Synclinal Curves. Theories to explain Lateral Movements. Creeps in Coal-mines. Dip and Strike. Structure of the Jura. Various Forms of Outcrop. Synclinal Strata forming Ridges. Connection of Fracture and Flexure of Rocks. Inverted Strata. Faults described. Superficial Signs of the same obliterated by Denudation. Great Faults the Result of repeated Movements. Arrangement and Direction of parallel Folds of Strata. Unconformability. Overlapping Strata.



CHAPTER VI.
DENUDATION.
Denudation defined. Its Amount more than equal to the entire Mass of Stratified Deposits in the Earth's Crust. Subaerial Denudation. Action of the Wind. Action of Running Water. Alluvium defined. Different Ages of Alluvium. Denuding Power of Rivers affected by Rise or Fall of Land. Littoral Denudation. Inland Sea-Cliffs. Escarpments. Submarine Denudation. Dogger-bank. Newfoundland Bank. Denuding Power of the Ocean during Emergence of Land.



CHAPTER VII.
JOINT ACTION OF DENUDATION, UPHEAVAL, AND SUBSIDENCE IN REMODELLING THE EARTH'S CRUST.
How we obtain an Insight at the Surface, of the Arrangement of Rocks at great Depths. Why the Height of the successive Strata