pound, and it is obvious that the earth would soon become uninhabitable were there no means of removing it from the atmosphere. Nor is this all. As carbonic acid is fatal to animal life, in as great a degree is the oxygen of the air necessary for its support. But this oxygen is always withdrawn from the air as carbonic acid is formed; for carbonic acid consists of carbon and oxygen. Thus, in burning, ten cwt. of coal consumes 32,000 cubic feet of oxygen gas; so that this town of Manchester (calculating its inhabitants at 300,000, the round number of the former census) consumes, for domestic purposes alone, exclusive of the manufactories, no less than 23,614,285,714* cubic feet of oxygen, and sends into the air a like quantity of pestiferous carbonic acid in its stead. Again, each man consumes and corrupts, every day, twenty cubic feet of air; hence the population of Manchester, by the air consumed in breathing, corrupt 2,190,000,000† cubic feet of air every year.

But vast as these quantities may appear, let us consider what a fraction of the globe we form; and not to extend our ideas beyond what they will readily embrace; let us calculate what 100 million men (an insignificant portion of the population of the globe) will annually consume and corrupt of air.

One hundred million men, then, will render unfit for the support of animal life, every year, no less than 9,505,200,000,000 of cubic feet of air.

From such data as these, it is evident, that the air would soon be rendered unfit for the support of animal life were there no means by which it is retained in a state of purity.

This it is the duty of plants of perform. An All-wise Creator has connected the life of plants and animals most closely together, the one depending upon the other. It is, indeed, a wonderful link which associates the vegetable and animal kingdoms. Plants form the primary nutriment of all animals; for although there are certain kinds entirely carnivorous, still the herbivorous animals upon which they subsist receive their nourishment from vegetable matter. But, following the chain in its continuation, we discover that animals, on the other hand, furnish the food of plants. During their life, they constantly expire carbonic acid, and discharge from their system matter, which by its decomposition, emits ammonia into the atmosphere; whilst at their death, their bodies decay, and furnish the same substances to the surrounding air. Thus they afford food for

• The calculation is as follows:-It has been found that a small town of 7000 inhabitants consumes in fuel, for domestic purposes, 551 million cubic feet of oxygen.

+ The calculation is as follows:-Supposing that a man consumes 20 cubic feet of oxygen, each day, in the process of respiration, then 365 × 20=7300. Again, 7300 x 300,000 2,190,000,000.

those very plants, upon which they themselves subsist; thus also the destruction of an existing generation forms the means for the production of a new one, and death becomes the source of life.

Such is a brief outline of the intimate connection subsisting between the animal and vegetable kingdoms. So closely, indeed, are they bound together, that, in the present system of things, we could not conceive the existence of one without that of the other.

But very different seems to have been the arrangements which prevailed in former ages. Animals were not then created in number sufficient to supply the food of plants. And although we cannot affirm, or even suppose, that the animal kingdom was independent of the vegetable, we have evidence enough to show, that the latter was in no wise dependant for support upon the former. If it be allowed that the paucity of animal remains, even in the carboniferous strata, where plants so abound, proves that the balance betwixt animal and vegetable life now subsisting, was then unknown, we must suppose that the food of plants was then supplied from other

sources.

It matters not what vague speculations have been held regarding the cosmogony of the world. With these the chemist has nothing to do. His science treats only of matter and its properties. Nor can he, without ample demonstration, listen to specious notions propounded of the transformation of the elements of which it is composed, or admit these as a basis for induction. His science teaches him that there are fifty-five bodies on the earth, by the different combinations of which all the varieties of matter are produced; and further, in the present state of his knowledge, he must allow that all these elements were on the globe when its present position was assigned to it.

However different in intensity and in form may have been the causes which produced the mighty yet gradual revolutions of former times, we discover in them a close analogy to those of the present day. Hence we are not warranted in presuming that the food of plants and animals was different then from what it is now. So far only can we affirm, that the food of plants was received from other sources than at present.

The food of plants consists of water, carbonic acid, and ammonia. What proofs can we find of the existence of these in former periods of the earth's history? During the deposition of the primary strata, where as yet no traces of plants and animals have been found, it is evident that carbonic acid existed. The primary limestones furnish sufficient evidence of its existence. It is true that the partial and irregular distribution of these limestones prove that their deposition was due to limited and local causes; but this does not militate against the idea that the carbonic acid must have been generally diffused throughout the atmosphere. All the limestones of aqueous origin have evidently been deposited from a solution in water containing an excess of carbonic acid; for without this ex

cess carbonate of lime will not dissolve. Now, without entering into geological speculations, it seems to be pretty conclusively established, that the heat of the ocean was considerable during the deposition of the earlier of the primary strata. From the contortions in the laminæ of greiss, mica schist, and chlorite schist, the water from whence they were deposited appears to have been in a very troubled state, just as it is in the present day when in a hot vessel. Now, when in this hot state it could not absorb or retain in solution carbonic acid from the air. Only in those spots where local causes had reduced the heat, carbonic acid might be dissolved, and carbonate of lime formed; or, if pre-existing, brought into solution, and afterwards deposited. This heated state of the ocean might, in some degree, account for its saline impregnation. There is no evidence of land having existed during the primary period, and during the ages which constituted it, this heated water acting upon the rocks which formed the crust of the globe, would have a wonderful effect in promoting chemical combinations, and dissolving the various soluble materials contained in these rocks. In all strata of later origin than the primary, we find rock salt. Salt springs arise from the coal system-rock salt abounds in the new red sandstone. The Alpine salt works are in the oolitic system; those of Cardona in the greensand; and of Wieliczka in the tertiary rocks. (Phillips). But, as far as I am aware, rock salt is absent from the primary strata. This seems to indicate that the water had not obtained its full saline impregnation when those strata were deposited. And indeed, it seems not improbable, that during this era, the water obtained many of its soluble salts from the disintegration of the primary rocks.

But to return from our digression. The existence of the limestones proves that even in the primary period, carbonic acid existed. The peculiar smell which distinguishes hornblende, and various aluminous minerals, when they are moistened, is due to minute traces of ammonia contained in them. Now this smell is very perceptibly possessed by the hornblende schists, which accompany gneiss; and hence we have a right to conclude, that they absorbed this compound from the air, or from the water, during their deposition. There are many facts to prove that ammonia was formerly of inorganic origin. Not only is it a constituent of all aluminous and ferruginous minerals, but it exists in many natural products found in volcanic regions. Dr. Daubeny has supposed that all the carbonic acid and ammonia which now exists, or has existed in the atmosphere, may have been derived from the interior of the earth. He finds a difficulty in conceiving how the hydrogen and nitrogen could have been made to unite on the surface of the globe, and hence, draws them from its interior. But although we do not agree as to the source from whence the food of plants is derived, we both equally admit that the primary food was of inorganic origin.

But I must assume, for the present, on the supposition that these

bodies were original constituents of the atmosphere, that they both existed in the air, during the primary periods, or, at all events, antecedent to the secondary, in much larger quantity than they do now and the proofs are obvious. Consider the immense deposits of vegetable matter in the carboniferous strata. All the carbon and nitrogen of which this is composed must have been originally present in the air as carbonic acid and ammonia. The greatest part of this vegetable matter is carbon; and hence it follows, that, as the carbon of the carbonic acid was retained, and its oxygen liberated, the air of the present day must be much poorer in carbonic acid, but much richer in oxygen, than that of former ages. Dr. Daubeny denies the possibility of ammonia ever having been present in the air in much larger quantity than at present; and, in proof of his view, he cites the experiments of Christison and Turner, that of ammoniacal gas in air acts as a poison to the vegetable kingdom. To this it may be replied, that ammoniacal gas is never present in the atmosphere. It is always in union with carbonic acid as carbonate of ammonia; and it is well known that water impregnated with this salt in the proportion of 30: 1, is very beneficial to vegetation. One pound of rain water contains rather less than grain of carbonate of ammonia. Now, even supposing that the rain of former ages contained 800 times this quantity, it would not be prejudicial to plants, but administer to the luxuriance of vegetation. Again, it has been found that plants flourish with great luxuriance in an atmosphere containing as much as its bulk of carbonic acid. But the air of the present day contains only one volume of this gas in 2,000 volumes of air. Hence it follows, that the air of former ages may have contained more than 150 times this amount, without injury to vegetation. These facts are sufficient to prove that the air formerly may have been much richer in the food of plants. Brogniart believed this to be the case many years since, and founded upon this view some ingenious speculations. Doubtless an atmosphere with quantities such as we have mentioned, would prove fatal to animal life, but we will shortly show that the express duty of former plants was to prepare the world for the reception of animals, and finally, for that of an intellectual being. One question, then, only remains : from whence did the atmosphere receive this carbonic acid? Dr. Daubeny conceives by a gradual evolution' from the interior of the earth. He supposes that this carbonic acid was furnished to plants during their life—not that a certain amount was originally emitted into the great magazine of food-the atmosphere. But it is difficult to conceive that an All-wise Creator would have made the life of plants and animals dependant upon adventitious circumstances. And surely it cannot be averrred that the emission of carbonic acid from volcanic sources, would be regulated by a direct interposition of a Divine Providence. The vegetation of the globe did not at once spring into existence, but was as slow in its progression, as that of animals; so that during the ages, when a scanty vegetation

covered the earth, the carbonic acid must have been constantly accumulating. And if, at its commencement, there was sufficient carbonic acid for the wants of plants, in the course of ages it must have been accumulated in much larger quantities. So that even on this view we must admit, that the proportion in the air could not be kept in any constant quantity. But we do not see any strong reason to suppose that the original food of plants was evolved from the bowels of the earth; nor can we discover any strong objection to the hypothesis, that all the carbonic acid and ammonia from the beginning of time, were original constituents of the atmosphere. The nitrogen and oxygen of which the atmosphere consists were certainly not evolved from the interior of the earth; and yet upon the same grounds could this be affirmed, for nitrogen, like carbonic acid, is evolved from the volcanoes of the present day. It is indeed difficult to conceive from what stupendous magazines of carbon the carbonic acid of the air was formed, or how hydrogen became united with oxygen to form all the water which covers the earth, without the occurrence of such dreadful explosions as would dash the the present system of the world to fragments. Such stupendous operations of nature are as yet beyond the capacity of the human mind to fathom: just so with the ammonia. If we cannot comprehend the mighty power which deprived its elements of their elastic condition, we can only believe that that power is as yet undiscovered.

From all that has preceded we believe we are warranted in considering that the carbonic acid and ammonia in the air were original constituents of the atmosphere; and further, that in former ages, they were present in much larger proportion than at the present time. We have shewn that such an atmosphere would not be unsuitable for vegetable life, although it would, certainly, prove destructive to terrestrial animals. We have now to examine the economy of vegetable and animal life of former times.

The first certain proofs of organic life occur in the grauwacke series. It is certainly singular that animals occur in this series, where plants are not found. These animals are not merely zoophyta, but conchifera. Still we cannot suppose that sea weed did not exist to supply them with food; for the spongy texture of such plants make them prone to decomposition. The paucity of animal. remains at this period, and their very unequal distribution, indicate that the conditions necessary for the support of animal life were not yet generally established. As we reach the silurian rocks we discover that the conditions for organic life have become more favourable, and consequently we find a much greater variety of forms; but we are still struck by the paucity of vegetable remains. Doubtless these were present in quantity sufficient to supply food to the marine animals which existed, but their perishable tissues have yielded to the elements of destruction and disappeared. The upheaved land during the grauwacke and silurian systems seems to