The Students Elements of Geology | Page 8

Rocks of Monte Bolca.
Trap of Cretaceous Period. Oolitic Period. Triassic Period. Permian
Period. Carboniferous Period. Erect Trees buried in Volcanic Ash in
the Island of Arran. Old Red Sandstone Period. Silurian Period.
Cambrian Period. Laurentian Volcanic Rocks.



CHAPTER XXXI.
PLUTONIC ROCKS.
General Aspect of Plutonic Rocks. Granite and its Varieties.
Decomposing into Spherical Masses. Rude columnar Structure.
Graphic Granite. Mutual Penetration of Crystals of Quartz and Feldspar.
Glass Cavities in Quartz of Granite. Porphyritic, talcose, and syenitic
Granite. Schorlrock and Eurite. Syenite. Connection of the Granites and
Syenites with the Volcanic Rocks. Analogy in Composition of Trachyte
and Granite. Granite Veins in Glen Tilt, Cape of Good Hope, and
Cornwall. Metalliferous Veins in Strata near their Junction with Granite.
Quartz Veins. Exposure of Plutonic Rocks at the surface due to
Denudation.

CHAPTER XXXII.
ON THE DIFFERENT AGES OF THE PLUTONIC ROCKS.
Difficulty in ascertaining the precise Age of a Plutonic Rock. Test of
Age by Relative Position. Test by Intrusion and Alteration. Test by
Mineral Composition. Test by included Fragments. Recent and
Pliocene Plutonic Rocks, why invisible. Miocene Syenite of the Isle of
Skye. Eocene Plutonic Rocks in the Andes. Granite altering Cretaceous
Rocks. Granite altering Lias in the Alps and in Skye. Granite of
Dartmoor altering Carboniferous Strata. Granite of the Old Red
Sandstone Period. Syenite altering Silurian Strata in Norway. Blending
of the same with Gneiss. Most ancient Plutonic Rocks. Granite
protruded in a solid Form.



CHAPTER XXXIII.
METAMORPHIC ROCKS.
General Character of Metamorphic Rocks. Gneiss. Hornblende-schist.
Serpentine. Mica-schist. Clay-slate. Quartzite. Chlorite-schist.
Metamorphic Limestone. Origin of the metamorphic Strata. Their
Stratification. Fossiliferous Strata near intrusive Masses of Granite
converted into Rocks identical with different Members of the
metamorphic Series. Arguments hence derived as to the Nature of
Plutonic Action. Hydrothermal Action, or the Influence of Steam and
Gases in producing Metamorphism. Objections to the metamorphic
Theory considered.

CHAPTER XXXIV.
METAMORPHIC ROCKS-- CONTINUED.
Definition of slaty Cleavage and Joints. Supposed Causes of these
Structures. Crystalline Theory of Cleavage. Mechanical Theory of
Cleavage. Condensation and Elongation of slate Rocks by lateral
Pressure. Lamination of some volcanic Rocks due to Motion. Whether
the Foliation of the crystalline Schists be usually parallel with the
original Planes of Stratification. Examples in Norway and Scotland.
Causes of Irregularity in the Planes of Foliation.



CHAPTER XXXV.
ON THE DIFFERENT AGES OF THE METAMORPHIC ROCKS.
Difficulty of ascertaining the Age of metamorphic Strata. Metamorphic
Strata of Eocene date in the Alps of Switzerland and Savoy. Limestone
and Shale of Carrara. Metamorphic Strata of older date than the
Silurian and Cambrian Rocks. Order of Succession in metamorphic
Rocks. Uniformity of mineral Character. Supposed Azoic Period.
Connection between the Absence of Organic Remains and the Scarcity
of calcareous Matter in metamorphic Rocks.

CHAPTER XXXVI.
MINERAL VEINS.
Different Kinds of mineral Veins. Ordinary metalliferous Veins or
Lodes. Their frequent Coincidence with Faults. Proofs that they
originated in Fissures in solid Rock. Veins shifting other Veins.
Polishing of their Walls or "Slicken sides." Shells and Pebbles in Lodes.
Evidence of the successive Enlargement and Reopening of veins.
Examples in Cornwall and in Auvergne. Dimensions of Veins. Why
some alternately swell out and contract. Filling of Lodes by
Sublimation from below. Supposed relative Age of the precious Metals.
Copper and lead Veins in Ireland older than Cornish Tin. Lead Vein in
Lias, Glamorganshire. Gold in Russia, California, and Australia.
Connection of hot Springs and mineral Veins.
INDEX.
...
STUDENT'S ELEMENTS OF GEOLOGY.



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.
Of what materials is the earth composed, and in what manner are these
materials arranged? These are the first inquiries with which Geology is
occupied, a science which derives its name from the Greek ge, the earth,
and logos, a discourse. Previously to experience we might have
imagined that investigations of this kind would relate exclusively to the
mineral kingdom, and to the various rocks, soils, and metals, which
occur upon the surface of the earth, or at various depths beneath it. But,
in pursuing such researches, we soon find ourselves led on to consider
the successive changes which have taken place in the former state of
the earth's surface and interior, and the causes which have given rise to
these changes; and, what is still more singular and unexpected, we soon
become engaged in researches into the history of the animate creation,
or of the various tribes of animals and