beds are covered by an enormous mass of porphyry, varying in thickness from 1600 to 2000 feet. In the lower part of the bed, the porphyry becomes vesicular, and changes into an amygdaloidal basalt, containing crystals of augite. Basalt, associated with porphyry in enormous masses, often covers the primary mountains of the Andes. They are arranged in regular columns, which strike the eye of the traveller like immense castles in the sky. Porphyritic rocks may, in general, be regarded as more ancient than basaltic rocks, as porphyry most frequently occurs intermixed with, or covering, transition rocks, and basalt is most commonly associated with the secondary strata, which it either cuts through in the form of dikes, or covers unconformably. Sometimes it appears to have broken the strata confusedly, and to have enveloped large portions of other rocks. All the trappean rocks give decisive indications of an igneous origin, not only in the shapes of their masses, but in their action on the adjacent rocks. Where basalt is in contact with gneiss, it becomes nearly compact, and approaches to the character of hornstone; and where greenstone rests on sandstone or clay, these rocks have a red and burnt appearance, and a hardness superior to what they possess in other places. Where they cross the coal strata, and come in contact with the seams of coal, the substance of the coal is, for several feet, converted into soot. At a greater distance from the trap, the coal is reduced to a coke or cinder, which burns without smoke, and with a clear and durable heat. At the distance of fifty feet from the dike, the coal is found in its natural, unaltered state. The thickness of trap dikes varies from a few inches to twenty or thirty yards. The extent to which they reach across a country has seldom been explored beyond the mining districts. The longest in England extends from the western side of Durham to Berwick, in Yorkshire. These dikes are generally harder than the rocks they intersect, and, when the latter are partly decomposed, often remain, forming vast walls of stone, that rise above the surface of the ground. They also extend into the sea, and give rise to reefs of rocks; and, when they cross the beds of rivers, they form fords, and sometimes hold up the water, and occasion cascades, of which there are frequent instances on the river Tees. From these circumstances, it seems conclusive that basalt and greenstone (and the same may be affirmed of the other vari

eties of trap-rocks) were thrown out in a melted state, like lava, and poured over the surface of the ground. The frequent occurrence of trap-rocks forming isolated caps on distant mountains, was for a long time considered as opposing the hypothesis of the igneous origin of basaltic rocks; but a more attentive observation of such districts has established the fact, that these isolated caps are parts of continuous beds, which have, in remote ages, been excavated by valleys, in the same manner as the beds of other rocks, which frequently form isolated caps on detached mountains.-The occurrence of thick beds of basalt, divided into regular pentagonal or hexagonal columns, and disposed in ranges of vast extent and height, early attracted the attention of mankind, and gave rise to various theories respecting their formation. Few countries in the world present more magnificent deposits of columnar basalt than the north part of Ireland and some of the Hebrides. The Giant's causeway (q. v.), in the county of Antrim, constitutes a small part of a range of this description. The promontories of Fairhead and Borge, in the same range, are situated eight miles from each other. These capes consist of various ranges of pillars and horizontal strata, which rise from the sea to the height of 500 feet. From their abruptness, they are conspicuous, and form a pile of natural architecture, in which the regularity and symmetry of art appear to be united with the wild grandeur and magnificence of nature. Many of the columns in the ranges at Fairhead are 150 feet in height, and five feet in breadth. At the base, along the shore, is a wild waste of rocky fragments which have fallen from the cliffs resembling the ruins of enormous castles. At the Giant's causeway, the columns rarely exceed one foot in breadth and thirty in height. They are sharply defined, and the columns are divided into smaller blocks, or prisms, of one foot or more in length, which fit neatly into each other, like a ball and socket. The basalt is close-grained, excepting the upper joint of the column, which is often cellular. The columns usually have five or six sides; but some have seven or eight, and others only three. Beds of basalt that are not columnar, in some places lie over, and also under, the columns. The basalt of the beds is amygdaloidal. The columns at Fairhead are not articulated like those of the Giant's causeway; but blocks, which are of great length, lie flat on each other. The trap formation ap

: TRASTEVERE. (See Tiber.)

to it.

TRAVELS AND VOYAGES. Travelling has always been one of the means of forming the character for the business of life, and for promoting scientific knowledge. By travelling, the ancients prepared themselves to become legislators and philosophers, as, for instance, in the cases of Lycurgus, Solon and Pythagoras. He rodotus travelled to study history. The statesman and the man of the world, the scholar, the naturalist, the geographer, the physician, the artist, the merchant, the political economist, the soldier, &c., each has his own objects in travelling. Young men who travel extensively by way of completing their education, should be well acquainted with the ancient and modern classics, mathematics, the principles of trade, political economy, history, statistics and geography, and with one or more foreign languages. The main object of the tour should be, in the first place, well settled, and all others be made subordinate The young traveller should not strive so much to observe a great variety of things, as to learn accurately what is essential. (See Reichard's Guide des Voyageurs.) In the history of scientific expeditions, the five following divisions may be made:-1. The earliest age of the Phoenicians, down to Herodotus, 500 B. C. The Phoenicians undertook the first voyages of discovery for commercial purposes, or to found colonies. Their colonies did the same. Unhappily, the accounts of these voyages are very obscure (as, for instance, of the circumnavigation of Africa), or couched in figures (like the first navigation of the straits of Gibraltar), or entirely lost. We know but little of their discoveries out of the Mediterranean sea. They discovered the island Cerne (Arguin), on the western coast of Africa, the Red sea, Madeira, and the Tin islands (England); they imported amber (probably obtained in their dealings with the Jutes). Their caravans to Asia and Africa gave them a knowledge of certain countries, beyond what we now possess. The Tyrian colony, the powerful Carthage, undertook still more extensive expeditions of discovery; but they are forgotten, and their results have perished with the state itself.-2. The travels of the Greeks and the military expeditions of the Romans, from 500 B. C. to 400 A. D. The Greeks made journeys to enlarge the territory of science. Besides the earlier travels of Herodotus, who has given faithfully the results of experience, and besides the al

most contemporary voyages of the Carthaginians, Hanno and Himilco, we are acquainted with the voyage of Scylax of Caryanda, who lived about the time of the Peloponnesian war. About 300 B. C., Pytheas of Marseilles first instituted astronomical observations, to determine more exactly the situation of places: he undertook two expeditions to the north; but we unhappily possess only fragments of the accounts of them. He proceeded even to Thule (Thual, in Irish, signifies the north), probably Iceland, where the floating ice filled him with surprise, and north-easterly as far as the Dwina, which he believed to be the Tanais, connecting, like a canal, the North sea with the Black sea. Instructed by the accounts of Alexander's expeditions, and by the sight of the subjects which this king sent him, Aristotle enlarged the territory of geographical science. Soon after Alexander's death, the materials that had been collecting since Herodotus were employed by Eratosthenes, whom we know only from Strabo, who, 300 years after (A. D. 10), produced a new edition, as it were, of the works of Eratosthenes, in seventeen books. Since Alexander's wars, Asia, as far as the Indus and Ganges, had become better known, and the Greek Macedonian empires, that sprang up there, still farther extended the knowledge of it. The armies of Rome supplied, in this period, many materials for the knowledge of countries. Asia was directly known to them of India; they obtained a knowledge from Egypt by means of the commercial intercourse between the two countries; the northern part of Africa was opened to them from Egypt to the Niger; and in Europe they became acquainted with the peninsula of the Pyrenees, Gaul, South Britain, Germany as far as the Elbe, Dacia and Pannonia.-3. The expeditions of the Germans and Normans till 900 A. D. The migrations of the nations in the fifth and sixth centuries brought with them information respecting countries which had been unknown or merely the theatre of wild fictions. The Byzantines came in contact with many new tribes, respecting which its writers have left us much valuable information. The Arabians have done much for the more accurate knowledge of the earth by their campaigns, their commerce and their scientific investigations. The sword opened to them a portion of North-eastern, Central and Western Asia, Northern Africa and Spain; and their commercial expeditions, by sca and land, extended as

far as the Indian islands, China, and the interior of Africa; but they have done less for the scientific improvement of geography than for the knowledge of different nations. What the Arabs contributed by their conquests to this knowledge in the eastern part of the known world, the German tribes effected in the west, by coming in close contact with the more cultivated nations of the Western Roman empire. Farther to the north, the Normans did more than the Germans; for we are indebted to them for new, though but accidental, discoveries. In their voyages, they discovered the Faroes, Iceland in the year 861, Greenland in 982, the western coast of which was immediately occupied by Norman settlers; and, twenty years later, the Norman Björn, being driven to the south-west by a storm, discovered Winland (Wineland, so called from the wild grapes found there), probably the eastern coast of Labrador, with which the whole description agrees. The great Anglo-Saxon king Alfred, who died in 901, set on foot, about that time, two voyages of discovery under two Normans, viz. Other, who proceeded from Norway round the North cape into the White sea to Biarmen (Permia), and Wulstan, who went from Sleswick to the gulf of Finland.-4. Besides the commercial and military voyages of the Arabs and Mongols, the travels of the Christian missionaries and some Europeans, down to 1400, furnish much valuable information. Pilgrims undertook long journeys; the crusaders diffused a more correct knowledge of Sclavonian Germany and of Asia; and the popes even sent envoys to the Asiatic sultans, and subsequently to the khans of the Tartars, to avert the further advances of these hordes. Boniface did much for the better knowledge of Germany by his travels as a missionary in 775, St. Otho for Northern Sclavonia in 1124, and Ansgarius, who died in 865, for Denmark and Sweden. There were also individual secular travellers, such as John Mandeville of England, in 1327; John Schildberger, a German soldier, who was taken prisoner at Nicopolis, in 1396, by the Turks, and afterwards by the Mongols, and thus had an opportunity to become better acquainted with those nations. A hundred years before, about 1270, the Venetian Marco Polo travelled through all Asia as far as Cathay (China); and at the same time with Schildberger, the brothers Zeno, two Venetian nobles, undertook a journey to the north. -5. The fifth period (from the year 1418)

In

now begins with Henry the Navigator and Columbus; and we now first meet with voyages of discovery, properly so called. The invention of the mariner's compass, between 1250 and 1320, by the aid which it furnished to navigation, led to extensive voyages. The Italians, especially Venice and Genoa, first set the example; but their commercial jealousy has deprived us of much of the benefit of their acquisitions. Their commercial gains excited other nations to similar enterprises. The Portuguese wars with the Mohammedans made them acquainted with Africa, and the eagerness for further discovery was encouraged and guided by the Infant Henry the Navigator (q. v.), who pointed out the path to be pursued. Porto Santo, Madeira, the Azores, were discovered between 1418 and 1450; in the latter year, Senegal also, and, soon after, Arguin (the Cerne of the ancients). 1462, Guinea was reached; and, in 1486, Barthol. Diaz doubled the southernmost promontory of Africa, which he named the cape of Storms, but which his king, John II, called the cape of Good Hope. The Portuguese Vasco da Gama (q. v.) discovered the passage to the Indies around Africa in 1498; but Genoa continued to conduct its commerce through the ancient channels, and Spain was so much occupied with the Moors of Grenada, that the enthusiastic Columbus could no where obtain a hearing for his plan of seeking a new way to India towards the west. The Spanish queen Isabella finally gave him her support, and he put his project in execution. Oct. 12, 1492, he came in sight of land, which proved to be an island (the island of Guanahani, or St. Salvador). On his third voyage, in 1498, he reached the main land. About the same time (1497), Sebastian Cabot, an Englishman, discovered the coasts of N America, from Labrador to Virginia. In 1500, Cabral, driven by a storm, discovered Brazil; Bastidas discovered Terra Firma, and Cortereal visited Labrador and Hudson's bay. In 1512, Ponce de Leon discovered Florida, and Balbao crossed the isthmus of Darien, and came in sight of the Pacific ocean. It was now first known that a new continent had been discovered, separated from Asia by a vast ocean, in which it was deemed probable a second new world might exist. The learned Florentine Amerigo Vespucci (who died at Seville, 1512) now made Europe acquainted with the character of the newly-discovered countries by his description. In 1519 et seq., Fer

nando Magellan sailed round the southrn extremity of America, through the straits named from him, and discovered the western passage to the Indies. By degrees the interior of America emerged from obscurity; Cortez and Pizarro, Almagro, Cartier and Orellana, made the most important discoveries respecting it, from 1525 to 1541. More accurate information respecting the northern and eastern parts of America was furnished from 1559 to 1616 by Francis Drake, Frobisher, Heemskerk, Hudson and Baffin. Whether Asia was connected with America was as yet unknown; but, in 1648, the Cossack Semen Deshnew proceeded from the river Kolyma, around the peninsula of the Tchouktsches, through Beering's straits, to the mouth of the Anadir. What had been rendered tolerably clear by this voyage was reduced to a certainty, in 1726, by captain Beering, who proceeded from the river of the Kamtschadales, through the straits named from him, to the peninsula of the Tchouktsches. This was confirmed by several subsequent voyagers, and by Cook, in his third voyage. They and Vancouver explored more particularly the western coast of America. The North American revolutionary war made the country still more known; and much information was diffused respecting South America by the missionaries, such as the Jesuit Dobrizhofer, in Paraguay. The most light, however, has been shed on that part of the western continent by the travels of Alexander von Humboldt (q. v.), the prince of Neuwied (q. v.), and those of several Englishmen and Germans in Brazil. (q. v.) The expeditions of discovery into the interior of Africa have been less productive. The Portuguese explored those countries only which were situated near the coast, in the prosecution of their commerce with India. Prior to Vasco da Gama, the western coast was explored, and after him the eastern coast (since 1497); but they did not discover the Red sea till the sixteenth century, although they were acquainted with Abyssinia.-See Damien da Goes, De Rebus Ethiopicis, etc. (Cologne, 1574). Egypt was visited by pilgrims, but the knowledge of it remained, nevertheless, very imperfect. The south cape of Africa was particularly explored, indeed, by the Dutch; but farther to the north, the Swedes Sparmann and Thunberg first penetrated, afterwards Levaillant, and, finally, Lichtenstein. James Bruce travelled to Abyssinia and Nubia, 1768-1773; and his account of

the sources of the Nile was confirmed by Salt in 1809. A comprehensive plan for exploring the interior of Africa was projected, and has been hitherto pursued by the African association (q. v.), formed in England in 1788. Much light has been thrown upon particular countries by the travels of Burckhardt, Bowditch, Mollien, Campbell, as well as those of lord Valentia and Salt to Abyssinia, those of Belzoni, Gau, Menu von Minutoli, to Egypt, and those of J. R. Pacho to Cyrene, in 1824. In April, 1828, Caillié, a young French traveller, succeeded in reaching Timbuctoo (see Caillié, and Timbuctoo), and the Landers (q. v.), in 1830, traced the Niger, and discovered that it emptied into the Bight of Benin. (See Africa, and Niger.) Asia was first visited by the Portuguese, but subsequently chiefly by the English and Russians. As early as 1498, Vasco da Gama discovered the coast of Malabar; and, before 1542, almost all the south coast, with its islands, and even Japan, were discovered by the Portuguese. But the coast alone was known, till, in the middle of the sixteenth century, the English laid the foundation of their dominion in India, by which the interior of Asia has been opened to civilized Europe. Farther to the north, the Russians undertook important expeditions. In 1577, Siberia was explored by the Cossack captain Jermak Timosejeff and the Russian merchant Stroganoff. In 1639, Kopiloff reached the eastern coast of Asia, and soon after, Kamtschatka was discovered. Since 1745, the Kurile, and the Aleutian, or Fox islands, on the coast of America, have come to light; and in the north of Asia, Müller, Gmelin, Lepechin, Güldenstädt, Falk, and, above all, Pallas, have made the most important expeditions, under the patronage of the Russian government. After Lapérouse had already accurately determined the north-eastern coasts of Siberia, the Russians explored the Caucasus and the Caspian sea, by means of Gärber, Reineggs, Klaproth, Parrot, and Engelhardt; Golownin described his residence in Japan. The other regions of Asia also became better known; Arabia, by the travels of Carsten Niebuhr, who visited it under the direction of the Danish government, in 1761, to add to the means for illustrating the Bible; Persia, chiefly by those of J. Chardin, from 1664 to 1677, and, of late, by those of Morier and Ouseley; Cabul, by those of Elphinstone; Syria and Palestine, by means of pilgrims and explorers of antiquities. But the north of India