ENGLAND.

LONDON. ENGLISH CHANNEL.

PARIS.

FRANCE.

JURA ALPS.

FRANCE.

ITALY.

it does generally in Northern and Central Europe. The mineral products are numerous, presenting some of the best mining districts in Europe.

The geology of Switzerland is complicate: the central axes of the Alps, which are primary, are covered by the secondary and tertiary series, the latter in some instances at the height of four thousand feet above the

ocean, showing that these mountains have been recently elevated.

396. In Sweden and Norway, the older rocks predominate: chalk and the tertiary are also found, but the drift presents the most striking features. Gold, silver, and copper are obtained, but the iron found in the gneiss is the most important metallic product. The more recent rocks, the wealden, chalk, tertiary, and alluvial, compose the surface of Denmark, while the igneous rocks, greenstone and lava, abound in Iceland and the Faroe Islands.

397. Russia and Poland are vast plains, bounded by mountains of primary rocks. The silurian, devonian, upper secondary and tertiary strata oocur, covered to a great extent by the drift. Deposits of salt with gypsum are found in the permian and tertiary strata.

The numerous mountain ridges and vast plains of Austria present all the varieties of geological formations, and mineral products.

398. Northern Italy consists of extensive secondary and tertiary plains, sloping from the Alps; Mount Bolca is famous for its fossil fishes. The form of the peninsula depends upon the Apennines which are of limestone, while the sub-Apennine hills are of tertiary. The Apennines have been elevated several thousand feet since the tertiary period. The traces of volcanic agency are numerous in Italy. The marbles of Italy are celebrated for their beauty and variety.

The mountainous regions of Spain and Portugal consist of primary and secondary strata, the chalk being found at considerable elevation on the Pyrenees. Tertiary strata occur together with extinct volcanoes of that period. Rock salt is found in the cretaceous strata, and quicksilver in the clay slate.

AFRICA.

399. The Atlas chain of mountains separates the Medit erranean sea from the great desert; these mountains are composed of primary rocks, and the strata on their northern slope, in the Barbary States, are secondary and tertiary, into which trap rocks have been frequently intruded, and in which salt and gypsum are found.

Through upper Egypt, Nubia, and Abyssinia, occur primary rocks, granite, porphyry, syenite (so called from Syene) and limestone; drifting sands from the desert have encroached upon these territories, while extensive alluvial deposits have been made by the Nile in lower Egypt.

400. The western coast of Africa, for several degrees of latitude on either side of the equator, is composed of granite, syenite and the metamorphic rocks; the great quantity of gold formerly obtained here led to the designation of Gold

coast.

Central Africa is traversed by the mountains of the Moon, which are primary and basaltic. Much of the gold obtained on the western coast was derived from the metamorphic rock of this range. The secondary series also, including the cretaceous formation, with rock salt, are found upon the Northern Slope.

401. The Sahara or great desert is a plain, slightly elevated above the ocean, extending from the rocky hills bounding the valley of the Nile to the Atlantic Ocean, two

SIERRA LEONE

SECTION OF AFRICA.-(FROM BOUE'S GEOLOGICAL MAP.) -Fig. 169.

DESERT OF SAHARA.

NILE.

thousand six hundred and fifty miles in length and varying from seven hundred to twelve hundred miles in width. Its surface is loose sand, with intervening portions of gravel, pebbles, earth, and salt, and occasionally fertile spots-oases-watered by springs. No rain falls upon the desert. The chalk, tertiary rocks, salt, and shells identical with species still living in the Ocean, show that this is the bed of a great Mediterranean sea but recently

elevated.

402. Chains of mountains consisting of primary and secondary rocks bound the two coasts of Southern Africa, between which intervenes an extensive plateau or table land, which merges at the southern extremity in the Cape Mountains; the tabular appearance of these Mountains at the Cape of Good Hope is due to horizontal masses of sandstone lying upon granite.

The islands in the vicinity of Africa, the Azores, Canaries, Cape Verde, St. Helena and Bourbon are of igneous origin; the volcanic peak of Teneriffe rises one thousand two hundred and seventy-five feet above the ocean. The axis of Madagascar is a chain of mountains, parallel to, and of the same age with the coast chain on the continent, the Mozambique channel only intervening.

SECTION OF SOUTH AMERICA.-(Boue.)-Fig. 169.

SOUTH AMERICA.

403. The form of the South American continent is due to the position of the three mountain chains, the Andes running near the western coast from Cape Horn to the isthmus of Panama, a chain of small width but of majestic height, dipping rapidly towards the Pacific, but sloping on the east into level plains of great extent; the Brazil chain between the Rio de la Plata and the Amazon river; and the system of Parima and Guiana between the Amazon and Orinoco rivers. These mountains are primary and volcanic, covered by slates fossiliferous limestones and red sandstones of various geological ages. Coal and chalk are found at an elevation of thirteen thousand and fourteen thousand feet above the Ocean.

The extensive plains east of the Andes are so low, even near the foot of the Andes that a rise of one thousand feet in the Atlantic Ocean would submerge more than one half of the continent of South America. These plains are divided by the mountains and table lands of Parima and Brazil into three different basins differing in aspect: the Llanos, or grassy steppes of the Orinoco; the Silvas or woody basin of the Amazon covering an extent of two hundred and eighty thousand square miles; and the deserts and pampas of Buenos Ayres and