caverns may have been filled with mud by some subsequent and partial deluge of which, doubtless, many have occurred since the earth was inhabited by the human race.

The porphyry and trap rocks, which constitute so prominent a part of the surface in that part of Scotland which we inhabit, are situated in an inconformable position to the other, or irregularly interposed between them; though sometimes they seem to be associated with, and to alternate with, the primary or secondary rocks. They must have been formed at a different time from the primary and secondary strata on which they lie. They never contain any animal or vegetable remains, though such remains often occur in rocks with which they alternate, or which are situated very near them. They frequently cut through the other rocks in the form of thick walls or dykes; and when they thus pass through a coal-field, the coal in their immediate neighbourhood is usually deprived of its bitumen, and converted into coke, just as if it had been exposed to heat. These, and many other circumstances, which we have not room to enumerate, led Dr Hutton to conclude, that these rocks had been formed by heat, and that they had been forced up from below in a liquid form, and thus covered, or penetrated and deranged, the formations through which they passed. This opinion, after having been controverted with much zeal by the followers of Werner, has gradually made its way, and seems at present to be almost generally admitted by geologists.

The word porphyry signifies at present, a rock having a compact basis, through which are scattered crystals of some other mineral. The basis gives the name to the porphyry, and is either felspar, pitchstone, or claystone. In this country, it usually occupies the summits of the mountains. This may be very well seen in Ben-Nevis. The lower part of that mountain is granite, but the central cone is felspar porphyry. If we examine this mountain, we can scarcely doubt that the porphyry has been pushed up through the granite, and formed the summit. It seems to have made its way south, for the summits of the mountains of Glenco consist of the same kind of porphyry.

The curious dyke of pitchstone porphyry, called the Skure of Egg, in one of the Hebrides, constitutes another specimen of porphyry, that seems to have made its way to its present position in a fluid state. The same remark applies to the dykes of pitchstone porphyry at Brodik, in the Isle of Arran. They were doubtless connected with the great porphyry formation in the south of Arran, though tha connexion can no longer be traced. The claystone porphyry constituting the summit of the Pent

so conspicuous from Edinburgh, and so common in the

Ochil Hills, exhibits no trace of having ever been in a state of fusion. But in the Ochils, at least, the claystone porphyry is obviously connected with the felspar porphyry, and seems to pass into it; so that the relation of claystone to felspar is probably much closer than we at present suppose.

The word trap was first applied by Riman to a set of hills which occur in Sweden; and he gave them that name, he says, because the rocks of which they are composed broke in rectangular fragments like sandstone. Werner afterwards limited the signification to certain rocks distinguished by the hornblend which they contain. The most important trap rocks are greenstone, amygdaloid, basalt, porphyry slate, wacke, and trap-tuff.

Greenstone is a mixture of felspar and hornblend, or sometimes of felspar and augite. It is very common about Edinburgh; Salisbury Crags, the Castle-hill, the rocks of Inchkeith, and many hills on the south coast of Fife, consisting partly of it. It bears very unequivocal marks of having been forced from below, upwards, in a state of fusion, and of having made its way through the other rocks with which it is associated.

Amygdaloid is a rock containing almond-shaped cavities, usually filled with calcareous spar, and various specimens of the numerous tribe of zeolites in a state of crystallization. Sir James Hall and Mr Gregory Watt threw much light upon the formation of this stone, and of greenstone, by their experiments. It seems to have been subjected to a strong heat while under great pressure. Basalt and porphyry slate have a great affinity to greenstone, and have undoubtedly been formed under similar circumstances.

We cannot afford space to enter into the details which would be necessary to show that all these rocks have been formed by the action of heat, and that they have all been either in a soft state, or in a state of fusion. But the subject has so long occupied the attention of geologists, and the numerous objections of Werner and his disciples have been so carefully examined and so fully refuted, that we are not aware of any difference of opinion at present existing on the subject. All admit that the porphyry and trap rocks have been formed by heat, and that they have been pushed up from below; but probably at a time when the whole was either covered by the ocean, or subjected to an enormous pressure by means of incumbent rocks, which have since been removed.

Thus, since the earth was inhabited both by vegetables and animals, since the primary and secondary rocks have been deposited, it has undergone a partial, but prodigious alteration, by the action of heat. Immense tracts of melted stony matter have

been forced up, and have made their way over a great extent of surface. These alterations and catastrophes must have taken place before the earth became inhabited by the human race; otherwise, had any rational creatures existed on it, and escaped the devastations which must have taken place, some traditionary information concerning such tremendous occurrences must have been handed down to us.

From the preceding sketch, imperfect and limited as it necessarily is, some idea may be formed of the numerous changes to which the earth has been subjected since its original creation, and the vast number of ages which must have elapsed before it became fit for the habitation of man. Well may it be predicated of the Deity, that with him a thousand years are as one day, and one day as a thousand years! May not a similar series of changes be going on in the other planets belonging to the solar system; and may it not be possible that they are not yet so far advanced as in our planet; and may not this be the reason why none of them as yet is possessed of an atmos phere similar to ours?

ART. IV. Notes on the Bedouins and Wahabys: Collected during his Travels in the East, by the late JOHN LEWIS BURCKHARDT. Published by the authority of the Association for the Discovery of the Interior of Africa. 4to. London: 1830.

to

Traveller of our HOUGH all the works of this enterprising and unfortunate traveller have greatly contributed to the increase of our knowledge, it is in the posthumous publications which bear his name that we find the largest mass of interesting and curious information.

The observations contained in his first works on the backsettlements of Syria and Palestine, and on the rude and brutal slave-merchants of the Nubian Desert, cannot rival in interest those of the posthumous volume in which he has so fully unveiled the mysteries of Mahommedan pilgrimage.* An equal rank may be assigned to the present, which throws new light on a ráce, who have long stood single among the nations, retaining from age to age a character in which lofty virtues and odious vices are strangely combined. The volume embraces also a different, but kindred subject, giving the most ample and authentic account that has yet appeared of the Wahaby power, which was synind doidon

Jaido & le tuer aft * See No. 99, p. 164.

once expected to have changed the face of the East, and which probably, even in its fallen state, exercises some influence.

The first and largest part of the volume does not, as its title imports, constitute so much a regular discourse, as a series of notes collected to form the materials of one; and these notes, taken at distant periods, and under changing circumstances, sometimes repeat, and sometimes even contradict each other. Nevertheless, we think ourselves indebted to the learned editor for having given them just as they stand, without any thing which could modify or alter their character; and we shall make it our task to combine these scattered fragments into somewhat of a regular and connected shape.

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The Bedouins, or wandering Arabs, form a singular race, who, from the earliest records of history, appear to have existed exactly in their present condition, witnessing without sharing the successive revolutions of the world,the rise and fall of the greatest empires. They bordered on several of the nations, anciently most refined and enlightened; yet those classic writers who have left such graphic pictures of some forms of barbarous life, throw no light on the interior state of Arabia. They delighted chiefly to recognise that region by the scented groves and bright gems which adorn its happy southern border. The roving tenants of its mighty desert were known almost exclusively under that one aspect, in which, indeed, they are but too prone to exhibit themselves, as fierce and lawless plunderers, whose band, lifted against every man, drew forth from all a just and reciprocal enmity.

Various circumstances have concurred to afford the modern world a somewhat more intimate view of this remarkable form of society. The early pilgrims to the Holy Land, and the successive travellers who proceeded overland to India, had occasion to pass along the Arabian frontier. These expeditions afforded ample proof of the character of this people as warriors and plunderers; but occasions were also found to witness, how sacred was the pledged faith of the Arab, and how unbounded the hospitality bestowed on the unprotected stranger who entered his tent. Yet travellers in general only skimmed the surface of the desert, passing along with a fearful baste, ill, suited for minute observation. Niebuhr, to whom we owe the only elaborate account of this region, scarcely touched even the borders of Pastoral Arabia. He merely descended the Red Sea, calling at several of its ports; but, with the exception of Yemen, penetrating into none of the interior districts. The only narrative which brings us into full contact with the details of Arab life, is that of the Chevalier D'Arvieux, whose residence in the tent of a chief,

whom he dignifies with the title of Grand Emir, afforded materials for a very lively and graphic picture of Bedouin manners. His sphere of observation, however, was comparatively very limited. He not only did not penetrate into the heart of Arabia; be did not even reach its border. His communications were entirely with one tribe, who had advanced through Syria, and taken up their quarters in the pastoral environs of Mount Carmel.

Burckhardt did not go very deep into Arabia, nor did he enter the vast plains of Nedsjed, the central seat of Bedouin society. Nevertheless, he possessed a combination of opportunities and qualifications, which had not fallen to the lot of any preceding traveller. He traversed the whole of the desert border behind Syria and Palestine, and the wilderness of Sinai and Horeb, making everywhere those diligent and judicious enquiries for which he was eminently fitted. During his residence at Mecca and Medina, he saw an assemblage of tribes from every quarter of Arabia, and was enabled to obtain information from Bedouins, who came from the interior of the Nedsjed. He has thus not

superseded indeed the observations of a traveller who should penetrate into the heart of the country, but yet done much towards elucidating the manners of the Arabians, and communicating an idea of the real condition of that extraordinary people.

The co-existence of bold and contrasted features in the Bedouin character had been frequently observed; but it was not clearly perceived how these could combine with, and pass into, each other;-how the same individual, on a slight change of circumstances, was welcomed with unbounded hospitality, or mercilessly robbed and murdered. This is a point which our traveller has very narrowly scrutinized, and seems to have traced the relation between these contrasted features of the Arab character, with a precision to which none of his predecessors made any approach.

The boast of the Arab is his hospitality, a virtue generally prevalent among simple and secluded tribes, but certainly practised here on a large and liberal scale. The entrance of the most entire stranger into the Arab tent forms an occasion of jubilee; a lamb is killed, the neighbours are invited, and a festival celebrated. In some encampments the members are on the watch for travellers advancing along the desert plain, and he who has the good fortune first to descry one, raises loud shouts, and claims him for a guest; while conflicting pretensions, and even quarrels, sometimes arise about this species of property. An instance is given of one Schiech, who, being reduced to such extreme poverty, that he could not furnish a dish to unexpected guests, had his favourite mare tied and ready for the knife, when