Patagonia. These plains are of recent geological origin, and have furnished very interesting fossils. The tertiary strata are extensively developed in many localities, especially along the terraced coasts of Patagonia, and bordering the plains. Portions of the continent many hundred miles in length have been raised from beneath the ocean within the period of the shell-fish now living, which are found in the plains still retaining their colors. The volcanoes of this continent are among the most magnificent of the globe.

South America has long been distinguished for its mines of gold, silver and platinum. The diamonds of Brazil are obtained from the alluvium; other gems also are found in the rocks, as the topaz, emerald and sapphire.

CENTRAL AMERICA.

404. The Andes continue through Guatimala and Mexico in an irregular mixture of table lands and mountains, consisting of granite, gneiss and mica-slate, with a large admixture of lavas ancient and modern; secondary sandstone and limestone occur together with alluvial deposits along the coasts. Few regions of the globe rival this in intensity of volcanic action. The mines of Mexico which are in talcose and mica slates, transition limestones and porphyry, have yielded a large amount of gold and silver.

The mountains in the West Indies are similar to those of South America of which some of the ranges appear to be continuous; this fact together with the identity of the fossil remains of extinct quadrupeds, renders it probable that the West Indian Archipelago was once a part of the American Continent, the area of the Gulf of Mexico and the Caribbean sea having subsided at a recent geological period. Secondary and tertiary strata are also developed upon these

islands attended by the drift and alluvium. The islands are still subject to violent volcanic action, especially earthquakes, and extinct craters are common. The Pitch Lake in Trinidad is three miles in circumference and of unknown depth.

NORTH AMERICA.

405. The general structure of North America is simple; its form is due to the position of two mountain chains-the Rocky mountains running north-west, and the Alleghanies northeast, including one of the most extensive basins in the world, embracing three millions two hundred and fifty thousand square miles. The Rocky mountains are composed of primary rocks, covered by sedimentary rocks of various geological ages, intersected by volcanic eruptions, though active volcanoes are principally confined to the northern part of the chain and near the Pacific ocean. At the base of these mountains on the east lies a sandy desert four hundred or five hundred miles wide. Rock salt and salt lakes are found in its vicinity. The coal formation with its fossils of tropical character is found at Melville Island in 7440 north latitude.

The auriferous deposits of California are alluvial, the detritus of sandstones, limestones and slates, especially talcose slate, intersected by quartz and porphyry. The gold is also found in veins in these rocks. Cinnabar the ore of mercury, silver, platinum, iron, tin and lead are known to exist in this locality.

UNITED STATES EAST OF THE ROCKY MOUNTAINS.

406. The Alleghany or Appalachian chain of mountains separates the great Mississippi Valley from the Atlantic slope; it consists of a series of from three to five parallel ridges with intervening valleys. Extending into New Eng

Chalk.

Eocene.

SECTION FROM THE VALLEY OF THE MISSISSIPPI TO THE ATLANTIC, CROSSING THE STATES OF MISSISSIPPI,

VICKSBURG. JACKSON.

ALABAMA, AND GEORGIA.-550 MILES.-(Lyell.) -Fig. 170.

Chalk.

Coal.

Granite.

land these mountains form the substrata

of the geology of that region, of which the unstratified and metamorphic rocks form the principal part; limited portions of more recent sedimentary rocks overlie them, among which the new red sandstone is supposed to be recognized in the Connecticut Valley.

407. The Atlantic slope is very narrow at New York, but in its southern portion extends several hundred miles from the ocean. Upon this slope in New Jersey the new red sandstone is found, succeeded by the cretaceous formation, consisting of marls, limestones and green sands; the latter extend to Alabama. The coal in Virginia near Richmond is assigned to the Oolitic period. The tertiary series commencing on the coast of Massachusetts extend almost continuously along the Atlantic coast into the Mississippi Valley; in the Carolinas, Georgia, and Alabama, they are extensively developed, furnishing many characteristic fossils, which are however very rarely specifically identical with the tertiary fossils of Europe.

408. The tertiary rocks constitute the principal part of the surface in the Southern states; they repose upon the cretaceous, and in the lower portion of the Mississippi Valley, these together with

the alluvium overlie the paleozoic strata, as is shown in the section, Fig. 170; in which

1 indicates the modern alluvium of the Mississippi.

2. The ancient fluviatile deposit with recent shells and bones of extinct mammalia; loess.

2* Marine and fresh water deposits with recent sea shells and bones of extinct land animals.

3. The Eocene with remains of the Zeuglodon.

a. b. Terraces.

4. Cretaceous formation, gravel, sand, and argillaceous limestone.

5. The Paleozoic-coal measures of Alabama.

6. Granite.

409. The stratified formations of the Mississippi valley and the western ridges of the Alleghany Mountains are the older-paleozoic rocks, which are expanded to a vast extent, and of very great thickness, while the secondary formations with the exception of very limited portions of the cretaceous, are deficient. Tertiary and alluvial deposits also extend up the valley of the Mississippi and its tributaries. The strata resting upon the primary rocks over large areas are the Silurian and Devonian. The carboniferous limestone is known to be widely extended in this valley, and the coal formation appears in many localities. These strata have frequently but little inclination, but are of great thickness, and abound in characteristic organic remains.

The identity of the great systems of the paleozoic rocks in Europe and in the Mississippi valley is easily recognised; that of the minor subdivisions is however, in many instances, obscure. The thorough geological surveys made in some portions of the United States whose rocks belong to these systems have led to the adoption of some provisional terms

based upon certain peculiarities of the rocks, or upon the localities where they have been investigated. The subdivisions of the systems made by the New York survey, constitute, for the present, a convenient standard of reference. The following tabular arrangement, by Professor James Hall, exhibits the correspondence of these systems in Great Britain and New York.

TABLE.

SUBDIVISIONS OF THE ROCKS OF
THE NEW-YORK SYSTEM.

Old Red sandstone

Chemung group.

Portage group.
Genesee slate.
Tully limestone.
Hamilton group.
Marcellus shale.
Corniferous limestone.

Onondaga limestone.

Schoharie grit.

Cauda-galli grit.

Oriskany sandstone.

Upper Pentamerus limestone.

Encrinal limestone.

Delthyris shaly limestone.

Pentamerus limestone.

Water-lime group.

'Onondaga salt group.

Niagara group. Clinton group. 'Medina sandstone.

Oneida conglomerate.

Grey sandstone.

Hudson-river group.
Utica slate.

Trenton limestone.

Birdseye and Blak-river lime

stones.

Chazy limestone.

Calciferous sandrock.

sdam sandstone.