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LESSONS IN GEOLOGY.-No. XLIII.

BY THOS. W. JENKYN, D.D., F.R.G.S., F.G.S., &c.

CHAPTER IV.

your attention. Ask yourself, what comes, then, of all the vegetable masses, and of all the animal matter, that rot in forests and woodlands, every year, over the extent of the globe? The answer of science is, that a portion of this vegetable and animal mass is volatilized into the air, and that the rest is carried away by

ON THE INFLUENCE OF ORGANIC AGENTS UPON THE running water, in which it either sinks into the earth, or flows

EARTH'S CRUST.

SECTION I.

ON BOTANIC AGENTS.

In the course of our lessons, the first three chapters have taught you the operations of fire, of water, and of the atmosphere, upon the earth's crust. This fourth chapter, which is also the last, is intended to illustrate the effects of vitality, in the forms of vegetation and animal life, in the changes which have been produced on the surface of the earth.

The business of this lesson is with the agency of plants, and with the effects which their growth and decay produce on the earth's crust. In this inquiry, we are not to limit our observation to the surface of the dry land, but to extend our survey to the

towards the sea. By this process, the same ingredients enter again and again into the composition of a variety and a succession of organic beings in vegetable and animal life.

It is well known that thousands of carcasses of terrestrial animals, and immense forests of drift timber, are every century floated into the sea, where both are imbedded in subaqueous deposits. Nevertheless, the vegetable mould on the earth's surface is kept in equilibrium. The principal elements tha chemists have found in plants are the three gases, nydrogen, carbon, and oxygen. Vegetables and animals derive them from water and trom the atmosphere. But whence do water and the atmosphere derive them, in order to supply plants with them? They derive them from the putrefaction of vegetable substances and animal matter, from the decay of rocks as the result of weathering and abrasion, and also from the agency of mineral

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larger portions of the globe which are under water, and which springs, which bring constant supplies from the interior of the are extensively covered by aquatic plants.

1. PLANTS AND TREES.

The quantity of plants, shrubs, bushes, and timber that grows on most lands, and especially in tropical forests, in the course of one century, must be enormous. Were these masses of vegetation deposited in a sea, they would pile up into a hill of considerable size; but though timber grows and decays for thousands of years, yet no such wood mountains are found to pile on the sites of forests, even within the tropics. It might have been expected that the masses of solid matter which are every day derived from the decay of terrestrial plants and animals would contribute to augment the amount of soil on the earth's surface. It must, therefore, awaken your surprise, when you learn that the vegetable mould which clothes the globe does not grow in thickness. This statement ought to awaken not only your surprise, but

VOL. IV.

earth.

In our chapter on Aqueous Agency, we considered the tendency of running water to scoop out gullies in the soil, and to carry the detritus towards the sea. This operation of streams and rivulets is counteracted by the power of vegetation. Vegetation counteracts the operations of running water in two ways. 1. It is in some degree antagonistic to the transporting power of rivers, and may be considered as reconstructive. The agency of vegetable life, by absorbing various gases from the atmosphere, causes a large mass of solid matter to accumulate on the surface of the land. Such a mass must, alone, constitute a great counterpoise to all the earthy detritus transported by the aqueous agents of decay. 2. The influence of vegetation is conservative, and tending to retard the waste of land. You constantly witness in a field, where a rivulet flows from a well, that the green sward through which the water runs prevents the soil from being 81

carried away. Upon sloping ground, also, it is seen that a covering of herbage protects the mould from being transported by rains, or being washed away by running water. As a further illustration of the conservative influence of vegetable life, it may be remarked that it also prevents loose sand from being blown away by the wind. In this case, the roots bind the separate particles of the soil together into a firm mass, and the leaves intercept the rain-water so as to make it dry up gradually, instead of rushing in a mass, and with velocity, upon the soil below.

That vegetation tends to preserve the mould that covers the earth, is evident from the observations which antiquarians and travellers have made on the increased removal of land that always takes place, after the clearing away of the woods that covered them. This is especially the case on the removal of woods that clothed the steep declivities of a mountain. In every such instance, the quantity of sand and soil washed down into the nearest river has increased enormously. The reason is, that as soon as the bushes and the trees are removed, the rain-water rushes with unbroken force upon the ground, flows off more rapidly, and sweeps away the soil and gravel.

II. PEAT AND MOSs.

Peat has not only a conservative influence to protect the underlying soil, but it has a reconstructive power, by which it augments the mass of vegetation on the earth.

Peat is not the product of any one species of plant, but consists of any herb or moss that is capable of growing in moist and cold situations, and that has also the property of throwing up new shoots at its upper part, while its lower portions are decaying. Peat, as the remains of dead plants, is a product intermediate between vegetable matter and lignite. It is first a plant, and it is turned into a lignite by a gradual and prolonged action of the water that covers it.

III. SEA-WEEDS AND FUCOIDS.

The "unfathomed caves of ocean" bear not only "full many a gem," but also full many a plant. Beneath the surface of the latitudes and longitudes, wherever a ray of light can penetrate, mighty sea, a magnificent vegetable world extends through all This world of vegetation is more wide-spread than the verdant covering of the dry land.

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Marine plants are exceedingly numerous, but they are divided into two great classes, or groups. First, the jointed kind, which embrace the species called CONFERVE, very small plants which the disjointed group, consisting of such sea-weeds as dulse, laver, consist of simple tubes-some of them even microscopic. Secondly, wrack, and all the gigantic species which either luxuriate in submarine forests, or float like green meadows or boundless prairies, in the ocean.

The sea-weeds that grow in comparatively small depths near the shore, are both the most limited in number, and the least extensive in distribution. The fuci that grow at the greatest depth of the ocean are both the greater in number, and the wider in extent of range. This circumstance suggests a correspondence of latitude, in the amount of vegetation, between height on land and depth in the ocean. On land, the lower the height or the latitude is, the more luxuriant is the growth of trees. And, in the ocean, the greater the depth, the more abundant is the growth of marine plants.

Beds of peat are seldom, perhaps never, found within the tropics. Even in Spain and in the south of France they very rarely occur. In proportion as you advance from the tropics towards the north, beds of peat become more frequent, and its sub-which are attached to them. Secondly, a very large number of stance becomes more inflammable. This is also time in latitudes between the tropics and the south pole.

The depth of peat soil and the number of peat bogs depend on the physical condition of the district. On the declivities of mountains, the depth of a peat bed rarely exceeds four feet. But in low and bollow grounds, into which peaty matter is constantly carried down by running water, the depth of a peat bog becomes forty feet and more. The extent of some of these bogs in the north of Europe is enormous. On the Shannon in Ireland there is a bog, that is fifty miles long and two or three miles wide. In France, between the city of Nantes and the sea, there is, about the mouth of the Loire, a bog that is one hundred and fifty miles in circumference.

or moss,

Many of the peat mosses are known to occupy the sites of ancient, forests of pines and oaks, some of which have disappeared even thin periods of history. Such bags are formed by the fall of trees, and by the stagnation of water. Had these trees fallen in warm climates, the woody matter would be removed either by insects or by putrefaction; but, in Europe, having fallen in low or moist situations, they are preserved by water.

The agency of peat mosses is not always conservative of the surface soil. In some districts where the climate is cold and moist, bgs occasionally grow to be agents of destruction. A peat bog acts like a sponge. It absorbs water in large quantities, and swells to the height of many yards above the surrounding soil. The capillary action of the turf fibres enables it to retain the fluid for some length of time, but not for ever. It frequently bursts, and then a violent inundation follows, and the muddy torrent, as instanced more than once in Ireland, scoops out ravines in the slopes of hills, bears away blocks and timber, and scatters them over the plains, or deposits them in the nearest lake or sea.

If such a moss bursts near an arm of the sea, that part of the sea becomes the receptacle of drift peat. On many coasts in the Baltic Sea and the German Ocean, we constantly meet with sections in which alternations of clay and sand with differ.ayers of peat are of frequent occurrence. At the bottom of many of the mosses in Holland, the remains of ships, of oars, &c., have been found; and in the valley of the Somme in France, there was found, in the lowest tier of the bog, a boat loaded with bricks. These two facts prove that, at one period and that very late, these mosses were navigable lakes or arms of the sea.

The seeds of marine plants are produced in their native element; they can therefore remain immersed in it for an indefinite period without any injury to their power of fructification. This fact enables us to account easily for their wide-spread diffusion in every zone where uncongenial climates or contrary currents do not interfere with their distribution. Sea-weeds have well-contrived facilities for sowing themselves over the body of the ocean. First, they generally have hollow pod-like receptacles in which their seeds are lodged. These pods give them buoyancy for floating. Other seed vessels have this power of floating in consequence of filaments species are enveloped with mucous or adhesive matter, like that which surrounds the eggs of fish. This mucus not only prevents them from injury, but serves to attach them to rooks or to floating bodies. These Bea-weeds fix their roots to anything and everything, to stones, to wood, or to other sea-weeds. This circumstance shows that they must derive all their nutriment from the water of the sea, and from the air contained in the water. Thirdly, naturalists have shown that these thalassophytes, or seaplants, are what is technically called proliferous; that is, they are so full of power to propagate their kind, that the smallest fragment of a branch of them can develop itself into a perfect plant.

Some of the gigantic sea-weeds grow up to the surface of the ocean, and appear like green meadows of immeasurable extent. These occur on each side of the equator in the Atlantic, Pacific, and Indian Oceans. The most extensive bank in the Atlantic is a little to the west of the meridian of Fayal, one of the Azores, between 35 and 36° off north latitude. When COLUMBUS camé to it, he compared it to a vast inundated field of grass, and he states that the weeds were so thick as to retard the progress of the vessel. This part of the Atlantic is called Mar de Sargasso, It includes two banks of Fucus connected or the Gulph-weed sea.

by a transverse band of Fucus natans, or floating sea-weed, and occupies a space larger than the whole surface of France. From the time of Columbus till now, that is, for three centuries, the situation of this great accumulation of sea-weed, whether resulting from the local character of the sea bottom, or from the direction of the gulph stream, has remained precisely the same.

Of this seaweed, called Sargassum bacciferum, two new species have been lately discovered by navigators in the southern seas. One, called Macrocystis pyrifera, is of gigantic size and covers a vast extent. The other is called Laminaria radiata, and forms vast meadows off the Cape of Good Hope, and in the Atlantic Ocean. Specimens of both of these weeds have been taken up, measuring 300 and 400 feet long. Some of them have been reported to be 1,000 and even 1,500 feet long. They are found in the open sea, hundreds of miles from land. Around Kerguelen Island, the two weeds form a great part of a band so thick that a Near California there boat can scarcely be pulled through them. are fields of them so dense and so impenetrable, as to have saved many vessels from shipwreck when criven by heavy swells towards that coast.

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present themselves as arborescent plants with branched trunks, sixty or seventy feet high. The third kind of vegetation is that of horse-tails, or the Equisetacea, distinguished in the engraving by having jointed and furrowed trunks and branches. With us, the largest plants of this kind attain but a very few feet in height, but in the coal measures they are found with arborescent or tree-like trunks, ten feet high and five or six inches in diameter. These three families of plants form about three-fourths of the vegetation of the coal period. The remainder consists of cone-bearing trees, and of vast quantities of a kind, apparently, like the cactus. Of the entire number of species discovered in the carboniferous rocks, two-thirds belong to a vegetation like the Fern.

You have now been introduced to the agency which vegetation exerts in the formation and in the conservation of the soil that forms the green surface of the earth. The principles and the facts which have been thus briefly intimated, you must now apply not only to the superficial covering of the globe, but also to the structure of the crust of the earth, as formed at different geological periods. As you walk or ride over plains or mountains, an entire vegetable world may be lying in ruins under your feet. In these coal forests, there were no plants bearing flowers, no Geology has demonstrated that, at different periods or epochs in trees bearing fleshy, juicy fruits, no kind of grass, and no birds. our world's history, vegetation has played a distinguished part, It used to be thought that it was a forest without a single living both in rank, luxuriance, and in extensive distribution. Differ-thing to move in it; but lately the skeleton of a reptile has been ent geologists have their respective systems for dividing the epochs discovered in rocks much older than the coal series. of ancient vegetation. M. ADOLPHE BRONGNIART divides them One remarkable characteristic of the vegetation of the coal into four. The first begins with the earliest traces of vegetable period is the uniformity or monotony of its plants. In our age life, and terminates with the coal formation. The second con- we find that different countries, in different climates, produce cludes with the .triassic. The third comprises the oolite and different plants; but, in the carboniferous era, the same plants grew Chalk. The fourth ends with the tertiary period. COUNT STERN-in Germany, Belgium, France, England, North America, and

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BERG, by uniting the second and third of these epochs, reduces the periods of ancient vegetation to three. His divisions are1. the vegetation of islands; 2. that of sea coasts; and 3. that of continents.

The earliest vegetation of the globe, and that which terminated in the carboniferous period, was simple but very magnificent. An ideal landscape of the earth during the carboniferous age is represented in fig. 97. Look at the forest represented in this engraving. The plants and trees are different from all vegetable products that you now see. There is nothing like it in the temperate zones, nor within the tropics. The vegetation consists of ferns but ferns not herbaceous as in our cold climate, but ferns which grow in the form of trees of considerable height, with palm-like, unbranched trunka. The next kind of vegetation is that of club mosses, or the Lycopodiaceae. With us, these club mosses are dwarf plants, small in size and few in number, but in the coal formations they

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Australia. This fact proves a remarkable uniformity of climat at that period. When North America was discovered, there were found in it only two wild plants that agreed with the vegetation of Europe. But of 53 kinds of plants found in the North American coal beds, 35 are common in the European coal fields.

However luxuriant this vegetation of the carboniferous era was, all the species of its plants, and almost all their genera, passed away before the second period of vegetation set in. A few ferns entered into the second era, but all the palms and calamites disappeared. The first flora, therefore, which was universally diffused over all the dry land of the ancient globe, was especially distinguished from the second, which is regarded as the flora of the triassic, the oolite, and the wealden, group of plants. This second family passed imperceptibly into the third, which comprises the plants of the tertiary formations. In the trias the characters of vegetation are altered by the complete disappearance of the cactus tribe, by a diminution of the proportion of ferns, and by

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the appearance of a few new species. Of this triassic vegetation very little is known, and what is known is generally classed with that of the tertiary. A few coniferous plants grew in the eras of the lias and the oolites, but they were not of the species that existed at the coal period. Immediately after the chalk period, a decided change took place in the features of the vegetation. The fern tribe still continued to diminish, but the cone-bearing wood increased in quantity. With the palms and other tropical trees, there grew willows, elms, poplars, chesnuts, and other similar trees, which increased in number and variety, till the flora of the more recent tertiary period had little to distinguish it from the vegetation of the present day. The contrast between it and the carboniferous flora, and the similarity between it and the present vegetation, are presented in fig. 98. In this landscape the woodland does not appear so strange and foreign to you as the coal forest did. This is very little different from the forest scenes of the present day. Among the trees we find the palm tree lifting up its feathered top, and a beautiful brushwood grows in all directions. The landscape is now varied; its outline is more uneven; and its aspect is more sunny. The forest is enlivened with quadrupeds that live on plants. Among these woods grew that remarkable pine tree, called Pinus succinifer, which produced the fossil resin called amber. This amber

is of immense interest to the geologist, as it often encloses specimens of insects, spiders, flies, small crustaceans, leaves of trees, &c., which are monuments of the flora and the fauna of that period. Upwards of 800 species of insects have been preserved in fossil amber. Amber is chiefly obtained from the brown coals of northern Germany, or the submarine beds of lignite found in Russia, and along the coast of the Baltic. These forests of amber pines grew in the south-eastern part of what is now the bed of the Baltic. As the amber found in the lignite and brown coal contains several fragments of vegetable matter, it has been ascertained that this tertiary forest contained four other species of pines, and several kinds of cypress, yew, juniper, oak, poplar, and beech.

The brief hints that have been given to you in this lesson upon submarine vegetation, and upon the formation of peat and drift wood, will prepare you for understanding the fucoid fossils which are found in ancient rocks, and for the vegetable remains found in the coal series. You have only to imagine layers of peat and deposits of drift wood to become bituminised, and the different seams of sand and mud between them to become consolidated by pressure from above and heat from below, to be able to account for their carbonisation, and for the structure of a genuine coal formation.

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LESSONS IN ENGLISH.-No. LXIX. By JOHN R. BEARD, D.D.

SYNTAX OF THE PREDICATE; THE VERB,-THE OBJECT.

'I MUST now conduct you to the predicate of a simple proposition. In order to effect my purpose, I must modify our model sentence a little, as thus:

Subject.

The sick man

Predicate.

drinks a beverage made of wine and water. The sentence thus altered brings under our notice two additional parts of speech, namely, the preposition (of) and the conjunction (and). It also directs our attention specifically to government, namely, in the relation borne by the verb drinks to the noun beverage, and in the relation borne by the preposition of to the noun wine and the noun water.

If, now, we look at our predicate, we find that it may be divided nto two parts, namely, the verb and the object; as,

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the past participle made; the preposition of; finally, the conjunc tion and. The articles have been already handled. The nouns, the verb, and the preposition range themselves under the general head of government; the past participle offers an instance of agreement; the conjunction acts merely in the way of combination.

Government—The Object after a Verb.

Every transitive verb has an object, expressed or understood, and the same verb may sometimes be used transitively or intransitively. If no specific object is given, the verb may be considered intransitive; e. g.,

the horse trots

Intransitive: Man drinks; Transitive. Man drinks water; the horse trots ten miles an hour; A verb which is strictly intransitive may be made transitive by a prepositional or adverbial suffix. To fly is intransitive, and to flyover is transitive; e. g.,

The eagle flew-over the summit of the mountain. Consider drink as intransitive, and append of, then you have The sick man drinks of pure water.

Drinks of is here a compound verb, and might be best written with the hyphen, thus, drinks-of. In this form, as being transitive, it has for its object pure water. But to drink, and to drink of, have not precisely the same import. We drink a glass of water, and we drink of a river. In fact, of has a partitive force, that is, it denotes a portion of; e. g.,

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