topaz, tourmaline, garnet, 2340 Scenery of a country affected

379

strata of the Barbary

States; Egypt, Nubia, Abys-

sinia,, dunes from the de-

sert, and alluvial of the

Nile,

Western coast, gold coast,
central Africa, mountains
of the Moon,

The Sahara, oases, recent-

ly elevated bed of the

sea,

Southern Africa, plateau and

table mountains; rocks of

the islands of igneous ori-

gin,

Form of South America, its

mountains, strata, exten-

sive plains and volcanoes,

its metalic products and

gems,

Cordilleras of Central Ameri-

ca, strata, volcanoes and

mines; West Indies, for-

mer connection with the

continent, volcanic agency,

Pitch lake,

General structure of North

America, mountain chains,

sandy desert, salt lakes,

coal in high latitudes; au-

401

8405

406

408

riferous rocks of Califor-

nia; other metals,

Alleghanies; New England

geology,

2399 Atlantic slope, its extent

and strata, new red sand-

stone, chalk and tertiary, 407

400 Tertiary rocks of the South-

ern States; section from

the Mississippi river to

the Atlantic ocean,

Strata of the Mississippi

valley, silurian, devonian,

cretaceous and tertiary:

identity with European

systems; subdivisions re-

ferred to those of the

New York survey,

Diversity of names applied

to members of the systems,

table of equivalence of the

lower strata in five States, 410

Numerous fossils; some ex-

tinct species of the higher

mammalia,

402

403

.

409

411

412

404 Mineral treasures of the Uni-

ted States; coal,

Iron, copper, gold, silver,

lead, salt, gypsum; no

volcanoes; hot springs, 413

FORNIA

GEOLOGY.

DEFINITION AND OBJECT OF GEOLOGY.

1. GEOLOGY is the Science which treats of the constitution and structure of the Earth.

Its object is to observe and describe the mineral masses, and the remains of organized bodies, animal and vegetable, which compose the globe; trace the successive changes they have undergone and discover the various laws that govern such changes.

Descriptive Geology exhibits the facts of the science;
Theoretical Geology attempts to account for them; and
Practical Geology shows their application to practical

purposes.

Subservient to Geology are— -Chemistry, which treats of the ultimate particles of matter, and their modes of combination; Mineralogy, which characterises and classifies the va rious minerals of which the earth is composed; Botany, and Zoology, which describe plants and animals; and Physical Geography, which relates the facts concerning the general distribution of matter at the surface of the earth-the forms and extent of continents and islands, river and mountain systems; together with the changes now occurring in them.

PLANETARY RELATIONS.

2. THE Earth is one of the planetary bodies constituting the Solar system-the third in order from the Sun-completing its circuit of 600,000,000 miles around that luminary in a year, and revolving upon its axis once a day. Its relations to the sun and other members of the Solar system determine its position in space, the amount of heat and light it receives, and consequently its vegetable and animal economy. A change in the position of its axis would alter its climate and the distribution of land and sea.