"There is, therefore, no difficulty in imagining the combustion to be kept up by means of silicon and aluminium, when once it has commenced, by the action of water upon the potassium, sodium, or calcium present.'

If this answer to our objections were as conclusive as it is undecided, imperfect, and objectionable, we might add, as a farther reason for our dissent, that many arguments might be gathered from the invasion it makes upon the laws which would govern the arrangement of a metallic nucleus; the improbability of water reaching it; the uncertainty whether atmospheric air could reach it; and the doubt whether any chymical action would be developed under great pressures;each of these might, and the sum of them would, lead us to the conclusion that the theory is doubtful, if not visionary.

Dr. Daubeny makes an admirable and comprehensive classification of the theories of volcanic action, when he says, "the theories which have been propounded with the view of accounting for the existence of volcanic action, may be divided into two classes-those which assume some chymical process, of which the heat is merely an effect; and those which, assuming the existence of the heat, deduce the other phenomena from its presence." We have explained the only theory worthy our attention, belonging to that class which assumes the existence of heat as an effect of the volcanic cause, and must now refer to the arguments by which those who maintain the primordial agency of heat defend their opinions.

That the earth's interior has a much higher temperature than its surface, has long been a prominent feature in geological hypotheses. But cosmogonists and theorists have not been satisfied with assuming a present condition, but have stoutly asserted the igneous fluidity of the primitive earth. It has been sometimes stated that the earth is a fragment of a body that was, at the time of partition, in a state of fusion; and this being assumed, its form may be readily traced to the diurnal revolution it is known to have, Sir William Herschel seems to have been enticed from his practical studies by a theory not less fascinating. This celebrated astronomer believed the earth to have been, at some past period, a mass of vapour, and attributes its present form to the condensation of the elastic fluid, an intense heat being given out during the process of reconstruction. It is not,

however, easy to comprehend either the philosophy of, or the necessity for, these theories, as there can be no reason why the Almighty fiat should not have called the earth into existence as an independent solid body, without the cumbersome machinery with which some philosophers seem to be so much delighted. But with such speculations we do not at present concern ourselves, as they cannot guide to an acquaintance with the cause of the phenomena already explained. It is sufficient to know that the interior heat does increase with the depth, a fact proved by a variety of experiments, and doubted only by those who wish to disbelieve it.

The earth is a reservoir of heat; and this agent exists with an intensity sufficient to produce the phenomena_ever attending volcanoes, earthquakes, and thermal springs. From the known effects of condensation, an increasing internal heat may be deduced, so that theory in this instance is confirmed by facts. There may be a modification beyond a certain depth in the ratio of increased temperature; but should future experiments establish the authenticity of this supposi tion, many objections now made to the theory, with what show of truth and honesty we do not say, will be effectually answered.

Those who differ in theoretical opinions too often imagine their theories to be diametrically opposed; but, when truth shall be discovered, it may be found that none of the causes zealously advocated by parties could of themselves produce the effects they are now supposed to explain. It is more than possible that neither internal heat, chymical action, nor electrical currents, could alone produce the volcanic phenomena; but, acting together, and they are known to be in some degree dependant on each other, they may give birth to all the violent disturbances that agitate the surface of the earth.

We have now attempted to explain the most important facts and theories in relation to the interior of the earth. It is not to be denied that there is much uncertainty and error in many of the speculations indulged and defended by the geologists of the present day, or that more extensive investigations will disabuse their minds of the fallacies resulting from an imperfect view of nature. The human mind may be admirably adapted to deduce principles from the information communicated by the senses, but if that information be inaccurate or partial, it will produce erroneous principles. A

variety of circumstances may prevent the accurate perception of truth, but especially prejudice, and a partial view of facts. These are even in the present day sources of error, for they still govern to some extent the reasoning of scientific men. We would not, therefore, force our opinions upon the reader, as though they were capable of the same rigid demonstration as a geometrical problem; we would rather have them considered as elements of thought than as dogmatical conclusions.

In the examination of the facts advanced in this chapter, there are two things which appear to us particularly evident, written, as it were, upon the face of every stratum that forms a part of the earth's crust; first, that a series of causes have acted in the production of rocks, differing from each other either in character, extent, or intensity; and secondly, that the condition of these rocks gives evidence of the existence of more violent igneous agents than are now in operation.

1. The beds forming the crust of the earth being distinguished from each other by mechanical and chymical composition, and each bed or suite of beds being remarkable for some organic remain peculiar to itself, there is evidence of the existence of secondary causes from the period when these rocks were formed; and the variety of agents supposes an interval of time between their successive operations. To imagine that a bed of sand and a bed of gravel could have resulted from the same physical force, or that there was not a perceptible interval of time between the deposition of a limestone, its disturbance by internal forces, and the formation of another bed upon the dislocated stratum, would effect as great an alteration in deductive reasoning as the volcanic force produced upon rocks. Great minds may be guilty of excessive folly in their effort to support a favourite hypothesis, and do sometimes resort to arguments they would condemn if employed by others. It has been maintained by some writers, who have had ample opportunities of examination as well as of reading, that a continuous series of causes, acting within a very short period of time, if not a single cause, produced all rocks, and occasioned all the disturbances under which they have suffered. The Mosaic deluge has been considered sufficient, both in intensity and period, to account for all the varied phenomena to which we have referred. But this supposition is opposed by facts too evident to be denied,

2. If the interior of the earth has a higher temperature than its surface, there is a probability that the ratio was greater when the ancient rocks were in the process of formation than at the present moment; and this is deduced from the abundance of igneous rocks, and the fact that heat is dissipated by radiation. In every age the volcanic force has been active, distorting strata, and ejecting among them igneous products; but it appears to have been most violent during the formation of the older rocks, a deduction that coincides with the supposition of a decreasing superficial temperature as the result of radiation.

But whatever opinions may be entertained after an examination of the earth's crust, it will be universally admitted that the arrangement of the mineral masses is not fortuitous, but the consequence of the same preordaining power that adapted all natural agents to aid in supporting life under pleasurable conditions. The sun may shine upon some worlds with an energy equal or superior to that with which it falls upon the earth, and it may diffuse over them the same vivifying rays; but if they are so constituted as to present a surface inapt to the reception of the life-supporting agency, then the solar rays, so far as these worlds are thus concerned, are useless. The earth is so formed, that it is suited to receive such influence from surrounding causes as is calculated to maintain life. It should ever be remembered that man acknowledges the display of Divine wisdom in the creation, because he perceives that in all parts of the mundane system there is an exact proportion between agents and the substances upon which they act.

CHAPTER IX,

LAND AND WATER,

THE superficies of the earth is estimated at two hundred million British square miles, and consists of land and water. Seven tenths of this surface are occupied by water, and a portion of the remaining three tenths is actually beneath the

level of the ocean. A large proportion of the dry land is situated in the northern hemisphere, the southern hemisphere presenting a broad and almost uninterrupted surface of water, the Pacific Ocean itself being of greater extent than all the dry land on the surface of the earth. Humboldt estimates the dry land between the tropics in the northern and southern hemispheres as being in the ratio of five to four, and without the tropics as thirteen to one, the northern hemisphere being the greater in both instances.

This relation between land and water has not, in all probability, constantly existed. The loftiest elevation upon the surface of the globe may have been at some past period beneath the level of the ocean, and the agent which elevated it may act, at some future period, upon the bed of the present ocean, and, raising it to the same elevation, entirely change the relative distribution of land and water. If it be denied that the dry land has been once beneath the water, how can the presence of organic remains in rocks be accounted for? It must not be supposed that the ancient shells found in rocks are merely distributed over their surface, for they form an integral portion of the beds, and are so disseminated through them that the rocks and the shells must have been deposited at the same time But that which was the bed of the sea is now dry land, and consequently one of two things must have happened: either the dry land that then was sank beneath the level of the ancient basins and received their contents, or the bed of the sea was raised, and the waters rushed into the newly-formed valleys. There can be no doubt as to which of these two causes produced the present relative condition of land and water. Rocks have been violently tilted from a horizontal to a highly inclined or vertical position; immense masses of igneous rocks have been ejected from the interior of the earth, and form, as it were, immoveable walls, against which the disturbed strata are piled in succession. Some local results may be due to depression, but all the great movements to which the earth's crust has been subject may be traced to elevation.

We need not refer to a very distant era, geologically considered, to find evidence of an alteration in the relations of land and water. The ancient beaches are among the most recent geological formations, and give, evidence of at least a partial, though by no means limited elevation, after the depo