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9. Serpentine; 10. Topaz rock; 11. Quartz; 12. Silicious shistus.
“ II. Intermediate mountains are composed of, 1. Limestone; 2. Trap; 3. Amygdaloid ; 4. Wacken.
“ III. Secondary mountains are composed of, 1. Sanda stone; 2. Limestone ; 3. Gypsum ; 4. Chalk; 5. Coal; 6. Common Salt; 7. Argillaceous Iron stone and Calamine; 8. Trap
" IV. Tertiary mountains are composed of, 1. Sand and and Pebbles; 2. Clays and Mud; 3. Bituminous Tufa.
“ V. Volcanic mountains emit, 1. Lava; 2. Pumice; 3. Scoriæ. The lava is sometimes mingled with felspar, quartz, or granite. If the mountain be a secondary mountain, marble, calcareous spar, gypsum, and similar substances are ejected."
DR. WALKER. “ These different series are tolerably arranged in regard to each other; the primary rocks forming the basis upon which the others rest: the transition rocks upon these primaries, are immediately recumbent, which are succeeded by the varieties of the secondary rocks, and by their detritus, constituting alluvial matters and soils. If the wind does not abate to-morrow, we may, perhaps, have time to go to Loch Neagh. This lake is worthy of notice from its peculiar qualities of turning wood into stone. Some of the ancient writers have gone so far as to say, that it would turn that part of the wood which was in the mud, into iron; the part in the water, into stone, while the part · above the water still remained as wood. Mankind delight in the marvellous, and in the early periods of the history of man, we have innumerable instances of the union of great wisdom and of great folly. Men, unaccustomed to search for natural causes, as in the earliest ages of the world, have invariably attributed
every uncommon appearance, to the production of invisible beings, such as fairies, genii, and so forth. As they advance in knowledge, they are apt to rush into the opposite extreme, and suppose that every thing contains within itself an all-sufficient power or cause, whereby it acts or is acted upon, without the interference of an all-wise and mighty Creator. I would wish you, Edward, not to rest content with hearsay intelligence, where you can from your own observation have the opportunity of judging for yourself. The most patient investigators have always been the most successful enquirers. Two of the greatest philosophers the
world ever saw, Lord Bacon, and Sir Isaac Newton, are in nothing so much superior to all other philosophers as in the deliberation and patience with which they pursued their enquiries. They sought for truth with the most unwearied diligence, they never adopted speculation for fact, nor were they satisfied with the semblance in place of the reality.
THE PETRIFYING QUALITIES OF LOCH NEAGů.
“ But to return to Loch Neagh," said the Doctor, * from which I have unconsciously wandered,--this lake is the largest in Ireland ; being twenty miles in length from the north-west to the south-east point, and nearly fifteen miles from the north-east to the south-west point. As to its petrifying qualities already mentioned, many writers suppose it consists, not so much in the lake as in the ground near it; that the earth in the vicinity of the lake does produce these petrifactions there is little doubt. The great Dr. Robert Boyle has observed that the earth harbours different kinds of petrescent liquors, and many of them impregnated with some sort of mineral or other.' But this petrified wood is found in the lake, and as there are no springs, or waters, but are more or less impregnated with such sort of mineral and saline particles, (this is proved by analyzing the most limpid streams) which after evaporation, still in the residuum, give some particles of salt, with some stones and mineral ores, Loch Neagh may produce these petrifactions as well as the earth in its environs.
“ Petrifying springs are generally impregnated, some with calcareous particles of stones, and others with ferruginous and vitriolic particles. Those of the stony and calcareous kind, when they drop on wood, or other vegetables, 'act on them for the most part by incrustations and coalitions, which yet adhere close together; they seldom turn the wood into stone; but sticking to it coagulate on it, and by degrees cover them with a crust of a whitish substance, of different thickness, by which the wood is wrapped in a stony coat, this cpát being broken before the wood is 'rotten, you will
find a cavity in the stone, which is very often filled by a subsequent incrustation or petrifaction, the stony particles then taking the place of the rotten wood. Sometimes, in. deed, these waters fermenting the pores of the wood, either longitudinally or transversely, insinuate themselves into them or 'fill them up with thin stony particles, and by their burning or corroding qualities proceeding from limestone, destroy the wood, and assume the shape of the plant they have thus destroyed.
* These petrifactions generally ferment with acids and spirit of vitriol, and by calcination may be reduced to lime.
“ Again, ferruginous or metallic petrifying springs, mostly aet by insinuating their finest particles through the pores and vessels of the wood, or other vegetables, without encreasing their bulk or altering their texture, though they greatly increase their specific gravity; and such is the petrified wood on the shores of Loch Neagh; for it does not show any outward addition or 'coalition of matter covering it, but preserves the grains and vestiges of wood; the only alteration perceptible is in the weight and closeness, and this is caused by the mineral particles which have filled up
.6s Though mines have not been discovered in the vicinity of the Loch, there is reason to believe there are such in its neighbourhood, from the great quantity of iron-stones found on its shores, and places adjacent to it, and from the yellowish ochre and clay to be met with in many places near it. If these iron-stones, 'which are very ponderous, and are of an ochrish yellow on the outside, and inwardly of a reddish brown, be calcined, they yield 'strongly to the magnet. That mines are generated, and 'found in the bowels of hills and mountains, is obvious to any person who has the least knowledge of metallurgy, and that springs also proceed from the same sources, is no less obvious"; therefore should a spring happen in any of these mountains to run through a vein of mineral-ore of any kind whatever, it will wash and dilute some parts of such mineral, impregnate itself with unctuous, saline, and metallic particles, if in its way, whether under ground, or at its issuing out of the cliffs of the mountains, of the sides of the river, or of the lake in question, it meets with wood, 'vegetables, or any lax bodies, lodged in the mud or gravel, whose pores by the natural
heat of the mineral streams, or any other accident, being open and duly prepared, these metallic moleculæ and saline particles will penetrate through, insinuate and lodge then. selves into the pores and vessels of such wood, and fill them up, and by degrees turn them into stone. There are some of these lapidescent juices of so fine a substance, yet of so petrifying a nature, that they will penetrate bodies of very different kinds, and yet scarcely, if at all, visibly increase their bulk, or change their shape and colour,
“ That such springs there are, hidden under this lake will appear probable, from what has been said, and perhaps evident, from the accounts since received, that in the great frost of 1780 the lake was frozen over so as to bear men on horseback, yet several circular spaces remained unfrozen. Mineral streams, or exhalations, highly saturated with stony and mineral particles, are often found to have a petrifying quality, as is seen at the bath called Green Pillars, in the city of Buda, in Hungary. If such streams should in certain places find or force their way through the sand or pores of the earth, they may operate on wood, &c. buried in the ground, permeate its vessels, and by degrees turn it into stone ; and such is the most probable, if not the only reason, that can be assigned for those petrifactions of wood found in sand.
66 Thus much for Loch Neagh, Edward, but I cannot quit this subject without mentioning those extraordinary petrifactions which are to be met with in a great desert to the west of Cairo in Egypt, mentioned by Mr. Horneman. He says, - that in the desert which forms a natural boun. dary to Egypt, on the west, extending from the Natron valley to the mountains Ummesogier, petrified wood is found of various sizes and forms; sometimes are seen whole trunks of trees of twelve feet in circumference, or more; sometimes only branches and twigs, scarcely any of a quarter of an inch in diameter, and sometimes merely pieces of bark of various kinds, and in particular of the oak. Many of the great stems yet retain their side branches, and in many the natural timber has undergone so little change, that the circular ranges of the wood are discernible. The colour of this
petrified wood is in general black, or nearly so, but in some instances it is of a light grey, and then so much resembling wood in its natural state, that their slaves would often col. lect it and bring it in for firing.'
+ These petrifactions are sometimes scattered in single pieces, but are oftener found in irregular layers or strata, covering a considerable space of ground.
“ The appearance of this desert waste in which these pe. trifactions are found, is that of a lee shore, over which the waters streaming before the storm have on their ebb deposited timber, or what else was carried away by the tide. No part of it has the appearance of having been worked by any kind of tool, and those trunks of trees which have been hastily pronounced by travellers masts of vessels, are nothing more than the branchless bodies of trees, thirty or forty feet long, which are in many parts splintered, but not by human workmanship. How this vast deposition of petrified timber came there, has not been decided, nor, most probably, will it ever be decided.
“ Many parts of these deserts are supposed to have been submerged at a period subsequent to the deluge, for there are in many parts marine shells of various kinds, found in the mountains which border upon it."
EDWARD.—" I think I should like to travel in Africa very much.”
Dr. Walker.-" You must then arm yourself with uncommon fortitude, the danger of traversing the interior of Africa is very great, and the fatigue such as those only accustomed to live like the hardy Bedoweens can scarcely endure. Nevertheless, what has been done may still be done, and I do think I should have some pleasure in accompanying you. And now before we leave Ireland let us take a slight sketch of its surface, climate, and productions."
GENERAL VIEW OF IRELAND.
The face of the country is mostly level, containing many bogs and lakes ; it is well watered with rivers, and has & small chain of mountains in Kerry, in Wicklow, in the south-east of Ulster, and in the north-west of Connaught: Croagh Patrick mount, on the south-east of Clew Bay, rises to 2666 feet above the level of the sea; Mount Nephin, in