and mixed with the fresh. This, I think, will be a sufficient caution to those gentlemen who may be about to build under similar circumstances.

DISSERTATION V.

ON THE SPECIFIC NATURE OF THE VEGETATIVE EARTH AND ITS SUBSTRATA.

"Naturalists have compared the structure of the earth to the coats of an onion. And the philosopher has shown that its form is oblong, like that of an elliptical egg, revolving on an imaginary axis; and supposes the centre of the earth to be about four thousand miles in depth, and eight thousand to the antipodes."-WHITHURST.

It surely concerns us all to know something of the ground we tread upon, of the country we inhabit, and of the sources and natural associations of the infinitely varied products with which the earthly world assuages our wants, increases our comforts, and multiplies the luxuries of life. The land or soil of the domain must therefore not be less considered than the situation of the mansion, or the nature of the air and the qualities of the water. This is far from being a trivial object, for both the air and water, which are allowed to be such important matters, are frequently, if not always, affected by it. We are therefore now to consider it in this light, and afterwards in regard to that which more immediately concerns its fertility, which is one of our chief purposes; though the strata for the foundation, on which the mansion is to be erected, demand an equal and serious attention, and we have already said, that in selecting an appropriate site for a dwelling-house, the gravelly foundation on account of its porosity is to be primarily preferred. We have seen that the air is influenced by unwholesome vapours arising from the earth, and the water by the strata through which it is distilled in passing through the crevices of the high ground, after it has fallen in rain: but these grievous occurrences, where they are frequent, generally proceed from a greater depth than is commonly understood. Happily for us this country is not much subject to the frequent maladies arising from long droughts or exhalations of malaria from marshes. But there is a point of consideration of that nature by which the soil is greatly and immediately affected; this is the loading of the air with moisture from detained waters secreted in the bowels of the earth.*

When we dig through the vegetative soil, we usually come to gravel, sand, or clay, or to a mixture of these unconsolidated materials; and in some countries we shall probably find nothing but marl or chalk at the greatest depths which we are able to penetrate. But in many places, after getting through the gravel and clay, we come upon stone, lying in layers or beds, sometimes horizontal at others inclined, parallel to each other, either of one kind, or of different kinds, according to the depths, and which would vary in different countries and in different places in the same country, as well as in its constituent parts, or in the same thickness, alternation, and position of its beds or layers. How long and in what degree the rains will be detained within reach of the surface, is altogether determined by the nature of the ground, its inclination, and the position of the substrata beneath, which

* We have shown that the earth is a round body, though of a somewhat flattened shape, like those larger pebbles on the sea-coast; the diameter from pole to pole being about twenty-seven miles less than that passing through the equator. Now more than three-fifths of the surface of the globe is covered by the ocean; and the land rises from the surface of the sea in the form of islands, and of great continuous masses called continents, without any regularity of outline, either where it comes in contact with the water or in vertical elevation; its surface being diversified by plains, valleys, hills, and mountains, which sometimes rise to the height of twenty-six thousand feet above the level of the sea. As different climates produce different races of animals, so they do different species of plants; but the substrata under the earth, as far as the nature of foundations, such as gravel and stone, are concerned, (which latter we shall treat of in the next section,) is independent of the influence of climate; the same substrata and rocks being found on the polar and in the equatorial regions. Although there is considerable diversity in the structure of the earth, it is not in any degree connected with the particular zones.-(G.)

may

come immediately under the architect's consideration in reference to the foundation of the house, as The lands or soils in England may be divided well as the fertility and healthiness of the spot. into three general kinds, loamy, sandy, and clayey, and the substrata below into gravel, marl, or a stratified rock, which are frequently found in layers inclining at different angles, and which be seen in the banks and sides of high roads throughout the different counties. The loamy is the best The sandy is the lightest and soil, and affords the most nutriment; containing vegetable matter. loosest, and the clayey is the toughest and heaviest, and not much esteemed by the agriculturist; these two last are the extremes. The loamy consists of earth, mixed with decomposed vegetable substances, and intermixed sometimes with sand and clay; it is therefore of a compound or middle nature between the other two.*

On positive gravel or rough sand there is always a healthy dryness in the air, particularly the former; but as to vegetation, if the latter is too near the earth it will let the rain soak through it too quickly, so that not enough of the moisture is detained for the common purposes of the growth of plants; and the dampness and sharpness of the air in higher situations, with this former soil, are too much for many constitutions. On the other hand, when the soil is of a thick tenacious clay, if it be in the extreme its strong adhesive power prevents the filtration of the water that falls in rain upon it from penetrating through. It is therefore detained too long, imparting a continual dampness round the house, causing it both to be offensive and unwholesome; here all is in the other extreme. If the clay lie upon the surface, it will be damp and slippery in wet weather, and crack and chop in dry; both of which are very disagreeable, and objectionable as to health and vegetation; and if it lie at a little depth under the surface, the rains, though they penetrate easily to it through the earth, are detained there for a considerable time, chilling the roots of the plants, and by that either rotting or stopping their growth, as well as preserving a continual swampy moisture.†

The loam, which is of a middle nature, and between these soils, is subject to neither of the previous defects: it receives rain freely, and detains it sufficiently, but not injuriously; there being enough moisture in the earth to soften by its vapours the great sharpness of the air, but not so much

*The crust of the earth is supposed to have been formed at different periods, each period is therefore called a formation. Primitive earth among ancient philosophers was one of the four elements of which the whole system of nature was thought to be composed. Earths are defined by Cronstedt to be such substances as are not ductile, mostly indissoluble in water or The earths are called primioil, preserve their constitution in a strong heat, insipid, and not dissoluble in boiling water. The celebrated compound soil of tive or simple, because they cannot be decomposed by any method hitherto known. The black colour of soils is the effect of putrefaction and decomposition. Campania in Italy, called pula, is black. It has also been remarked that the The influence of caloric is increased on a dark-coloured soil, the rays being absorbed. peasants of the Alps spread black mould over the surface in the spring to dissolve snow: it is well known that a black dress attracts heat and that a white repels it.-(Stovel.)

Now those various soils are generally peculiar to the different positions of the earth's surface; the clayey to the low ground, the loamy to the midland, and the sandy to high land. It is here we see the order of the universe, now so beautifully diversified with hill and dale, and the mountains that shade and fructify the valleys by their streams; for the valleys are more or less extensive furrows of the surface, ramifying generally to a considerable lateral extent, and independent of secondary purposes, fulfilling that most essential one of draining the adjacent lands of their water, and carrying it into brooks and streamlets, which gradually unite to form rivers, and ultimately convey their contents into the ocean, of which, in fact, they constitute a series of ascending branches. Is not this seeming disorder and confusion of hill and dale, which appears If all the evidently a part of the order and harmony of the universe, prepared progressively as a fit habitation for man? strata had remained horizontally, that is, parallel to the surface of the globe, it is clear that we should never have become acquainted with any other than the upper members of these series, and that the beds of coal, rock-salt, and the ores of the metals, all of which are confined to the inferior strata, could never have been made available for the purposes of man. Without this elevation of strata, the earth would have presented a monotonous plain, unbroken by the beautiful forms of With these irregularities of the surface are ultimately hill and valley, or the majestic and sublime scenery of mountains.

connected all the varieties of climes, and the diversified products of animal and vegetable life dependent thereon, as well as the whole of what may be termed the aqueous machinery of the land; the fertilizing and refreshing rains, the source of springs, inland lakes, and the course of rivers and brooks, in their endless ramifications of rivulets. Throughout all this reigns such a harmony that it is evident that the breaking up of the earth's crust is not an irregular disturbance, but a work of design, in perfect accordance with the whole economy of nature.—(Dr. Gregory's Elements.)

as to chill the roots of plants or occasion a dampness at the bottom. We have said that the architect is not required, like the physician, to select an air that will be suitable to particular complaints, but such air as, being pure and temperate, will preserve the health of the individual resident. This, so far as ground is concerned, is not an inconsiderable thing, there being a continual evaporation arising from it, and that will most naturally be found where the soil is loamy, and under which is a bed of gravel. Where there are lava and limestone beneath the earth, the air in winter is generally warm, arising from the gaseous and calcareous caloric of the stone; but in summer it is here oppressive. Granite rock does not produce the same effect; it is also of a less reflecting quality where it appears above ground, and the air is here more salubrious. All smooth marble-stones as well as metals reflect the sun's rays which fall on them, whereas more porous substances, such as freestones and bricks, absorb the rays to a great degree.*

Further, the earth still demands greater investigaton, namely, as to its richness and fertility; these are of the most immediate concern both as relates to profit and beauty of scenes: a flower-garden, for instance, is a very essential appendage to a country-house, and a kitchen- and fruit-garden at some moderate distance. Both these should be on such earths or soils as will cause things planted in them to grow well; for this there is none so universally fertile as the loamy; it admits, as we have said, the rains and dews to penetrate freely to the roots of the plants, and detains them there a sufficient time without injury. We see by observations in nature's wildest state, many instances of the general excellencies of this kind of earth; though there are some plants that thrive best in clayey soil, while others will not grow on sandy light earth; and there are some again that delight in sandy earth, and will not live in clays, and so on, vice versâ. Thus the rural poet remarks,

But both kinds will grow in a loamy earth; indeed, there is no kind of plant that will not thrive here unless it is aquatic. This fertility of the earth must not be confined exactly to the ground adjoining the house, but extend to all the estate or domain, as it is this which gives it a rich and verdant prospect. There is a cheerfulness and beautiful appearance in a fine upland woody country, particularly when it is bold and undulating, which is seldom to be found in the poor or barren, and hence in proportion to the goodness of the earth is generally the beauty of the face of nature.

* To afford warmth to plants growing in the earth is of considerable importance, and the power of accumulating and retaining it varies as much in soils as the proportions of their constituents. A rich black mould, containing one-fourth of vegetable matter, has been found to have increased in its temperature in an hour from sixty-five to eighty-eight degrees by exposure to sunshine, while a chalk soil was heated only to sixty-nine degrees under similar circumstances; but the first, when removed into the shade, cooled in half an hour fifteen degrees, whereas the latter lost only four degrees. This explains why the crops on light-coloured tenacious soils are in general so much more backward in spring, but are retained longer in verdure during autumn than those on black light soils; the latter attain a general warmth more readily, but part with it with equal speed. The following experiment, which has been successfully repeated upon light as well as tenacious soils, demonstrates how greatly the colour of a soil influences the accumulation of heat. Coal-ashes were sprinkled over half of the surface of beds sown with peas, beans, &c., and in these the plants invariably appeared above ground two or three days earlier, obviously on account of the increased warmth, it being a well-known fact that dark-coloured bodies absorb caloric more readily and in larger proportions than those of a light hue.-(Sir Humphry Davy.) Even a gardenwall that is coloured black will attract more heat than one that is white.-(A.)

In hot soils vegetables are hard and strong, but not prolific; in moist ones luxuriant and prolific, but neither strong nor hard. A good soil yields the most abundant harvest. In bad ones fruits have a purer juice, bees yield a better honey, game of a mor e delicious flavour, and wild-fowl more delicate and wholesome.-(Spectacle de la Nature.)

G G

The above character so certainly and perfectly accompanies the excellence of ground, that before it is opened for examination of its qualities, it may be known by the aspect or the growth of trees and the herbage. Where trees grow straight and beautiful, with freeness from moss, clearness of bark, and luxuriant in foliage, the earth is always excellent, for where it is faulty in quality or shallowness, it will be equally seen by the herbage on its crust, which will be poor, in spite of all the labour and expense that may be bestowed upon it, and the trees will likewise grow irregular and become stunted, and have the appearance of decay, though there may be other causes.*

After these observations, we would have the architect, when he is about to select a spot or situation for a house, to take into his most serious consideration the nature of the soil and subsoil; and the character of the surface should be one of his first objects of examination, with all the advantages of nature in the fullest extent, both as to its salubrity and fertility, as well as its diversified scenery of undulating hill, winding dale, wood, and water. However, he must not always expect that in any one place he will find all these combined in their most full perfection; but knowing what these perfections are and what is required, he will be the better able to judge how far an excellence in one kind will make an amends for a deficiency or imperfection in another, and how far the objectionable part is capable of being improved, if not perfected.

DISSERTATION VI.

A CURSORY VIEW OF GEOLOGY, IN REFERENCE TO THE ORIGIN, NATURE, QUALITIES, AND DURABILITY OF VARIOUS STONES USED IN BUILDING.

"To form an idea of the position of the different kinds of rocks which lie on each other below the crust of the earth, let a number of leaves of paper of several different colours be pasted one upon another; then bending them up together into a ridge in the middle, conceive this ridge to be again reduced to a level surface by a plane passing through the leaves so as to cut off all the parts that had been raised. Again, let the middle be elevated, and this would be a good general representation of most of the layers, if not all the large tracts of mountainous countries, together with the undulating parts adjacent. From this formation of our globe it will follow, that we ought to meet with the same kinds of earths, marls, and stones appearing at the surface in long narrow slips, and lying parallel to the greatest rise of any large ridge of mountain throughout the world, and so, in fact, we find them."-MITCHELL.

Having described the nature and qualities of the vegetative earth necessary for the growth of trees, herbage for cattle, the fruits for man, and the connected substrata essential to support the mansion, we shall now give a geological analysis of the formation, position, and qualities of different rocks in the earth, proceeding in an ascending order from the granite or primitive rock; noticing the leading character and peculiar quality of each group; and, lastly, treating on the durability of the different kinds of stone used in building, with a knowledge of which it is of the utmost importance and consequence, both to the employer and the architect, to be well acquainted; for

* In the southern parts of Devonshire, near the sea-coast, where the land is good, the trees are much cut on the western side by the winds that blow from that quarter, which is supposed to be occasioned by its long passage over the Atlantic Ocean, bringing with it the insinuating particles of the sea-air: the cause of this is not for our inquiry, but it has been a subject for curious investigation among natural philosophers in almost all ages, but still remains in great obscurity. There can be little doubt, however, that a large quantity of saline matter existed in this globe from the creation; and at this day we find immense beds of rock or common salt buried in the earth: but whether these collections have been derived from the ocean, and deposited in consequence of the evaporation of its waters, in certain circumstances, or whether the ocean was itself originally fresh, and received its salt from collections of saline matter situated at its bottom, or from that brought from the influx of rivers, cannot now be ascertained; but the sea has been found to vary in degrees of saltness at different parts of the world, and at different depths of the water. However, where it is most hot, there it is most salt.-(Watson's Chemical Essays.)

however beautiful a structure may be, if built with a fragile stone it will have to boast its beauty but a little while. Now durability was what both the ancient architects of Egypt, Greece, and Rome always aimed at in their works, and thus many of their edifices which still exist we find are constructed of the most durable materials; hence they have stood the storms of war, the tempest of the elements, and the corroding hand of time, and still bid fair to endure (unless doomed by fanaticism to destruction) until the general annihilation of all things,* when

"The gorgeous palaces, the solemn temples,
Yea even the great globe itself,

And all that it inhabit shall dissolve,
And, like the baseless fabric of a vision,
Leave not a wreck behind." SHAKSPEARE.

What the form or surface of our terrestrial globe originally was is beyond the power of human intellect to divine; but this not being important to our purpose, we shall at once proceed to observe, that the globe being formed by the Almighty fiat of Jehovah, and land and water separated,† it is supposed there were at this time certain rocks formed; that they were of one particular kind and in compact masses, deposited in certain parts of the world, and situated as deep in the earth as man has ever yet been able to penetrate. These primitive rocks have been found to be that of the granite kind, but varying in texture according to their compounds at different parts of the globe. This is called the primary formation.‡ Now since the earth's first formation it has evidently, whatever it might have been, undergone a great change, and produced secondary rocks of a stratified nature. These secondary stratified or transition rocks (as they are sometimes called,) comprehend a great variety of different beds of stone, extending from the primary strata upwards to the chalk, which forms the upper or most recent member of the division. As to their origin and the nature of their formation, it is supposed by the action of the elements on the primitive rocks their tops would decompose, and the débris, by the repeated rains, be then washed down into the hollows below, which, being there deposited, and mixed with shells and other matter, producing a thick mud, would ulti

* The Egyptian Memnon, formed of porphyritic granite, is as perfect as ever. The Parthenon at Athens, above two thousand two hundred years old, built of Pentilican marble, still stands, and though stripped and mutilated, shows no symptoms of decay. And the huge rotundical Coliseum at Rome, whose dimensions are six hundred and fifteen feet long, five hundred and ten broad, and one hundred and fifty-seven high, built by Vespasian in the first century, yet rears its stupendous and staged columnar front in the air.--(R. B.)

+ Burnet's theory of the earth was at one time considered an interesting conjecture, but like that of Buffon, it will not now bear the test of scrutiny. Burnet imagined that when the elements separated from the original fluid mass, the heaviest particles tending to a centre constituted a nucleus, upon which water and air afterwards assumed their respective stations. The air, however, was not as we now see it, a transparent attenuated medium, but it was loaded with exhalations and impurities, which it gradually let fall upon the surface of the waters, and then floated upon the whole in cloudless serenity. The deposited matter constituting a rich crust, sent forth its vegetable productions, and soon became clothed with uninterrupted verdure: everything was smooth, soft, and regular, and there was, he supposes, a universal spring, for the plane of the ecliptic was coincident with that of the equator. In process of time, however, the green and even surface now described, began to suffer from the continuous action of the sun's rays, which formed cracks and fissures, that ultimately extended to the abyss of waters beneath, and these being sent forth by elastic vapours expanded by heat, soon inundated the superficies; an universal deluge ensued, and on the violent shocks and concussions that attended it, rocks and mountains, all the irregularities of the present surface, had their origin; then the water gradually subsided into the residuary cavities, forming the ocean, and partly were absorbed into the crevices of the disjointed strata and nucleus; vegetation began to reappear, and the once uninterrupted and uniform surface was now broken up into islands, continents, mountains, and valleys. (Burnet's Theory of the Earth.)

It is very probable, says a more consistent writer, (Camden,) that the face of our globe underwent an alteration from the waters of the Deluge and other causes; that some mountains were thrown up, and many higher places sunk into plains and valleys; that bodies of water were dried up; dry ground became pools of stagnant water; and that some islands were torn from the continent, as appears by comparing Dover cliffs with those of Calais.-(See also Cuvier's Theory.) ‡ Geologists agree that there are certain rocks more ancient than others.-(Lyell's Elements of Geology.)