ceed volcanos and earthquakes. He will however permit me to obferve, that the caufes of volcanos and earthquakes are pretty well known to naturalifts, as, by the mixture of fulphur and iron with water under factitious mounds, they can imitate them very perfectly without the aid of extraneous fire (k). No fuch central furnaces are therefore neceffary to account for them. Mr. de Buffon imagines this globe to have been expelled from its parent fun in a ftate of fufion gradually cooling, but thence yet retaining a central fire, far below the bottom of the fea, which will at length like all terreftrial fire burn out. Dr. Hutton pretends this central fire to have burnt for millions of years, and to continue kindled for millions of years to come, notwithstanding those emiffions which have formed our metallic veins, and thofe which keep up our volcanos. It must either be that fame fiery fluid which is fuppofed to burn in the fun without fuel and without lofs, or he muft fupply it with pabulum. Unrestricted as to time, he thinks proper to employ the combustible matters, not of one but of two or more anterior earths, to feed his fubterraneous fire. This is pure imagination, but not philofophy. The fire which he fuppofes to have been burning for fo many millions of years muft in that time have confumed, calcined, or evaporated, the whole substance of this globe, and with it have expired. Notwithstanding these untoward objections, this deviation from his original is not without its ufe. From the well-known effects of entire fufion it has been demonftrated, againft Mr. de Buffon's theory, that the prefent ftate of thofe fubftances called primitive,

which he affirms to have been in fufion, fhews that their liquefaction by fire is absolutely impoffible. From the compreffion of fuperincumbent waters, Dr. Hutton endeavours to evade these natural and neceffary effects of fufion. This compreffion modifies all thofe effects. This he explains by the example of ftones thrown up by volcanos which appear to have suffered little in their texture, though liquid lavas may be at the fame time emitted. There feems no real analogy here. Whilft the matter compofing liquid lavas has felt the full effect of fire, and pumice ftones are greatly altered, these ftones appearing little damaged have undoubtedly been torn from the fides of the mountain by the inftant effect of the convulfion, and falling into the boiling caldron are thence immediately exploded. Dr. Hutton has to account for adventitious fubftances inferted without change in the interior, or for a great variety of diftinct fubftances forming, except the cement, the whole texture of folid bodies faid to have been in long and therefore perfect fufion. Can these erupted ftones which have barely touched the fire give the fmalleft explication of the heterogeneous appearances of immenfe ftrata pretended to have been liquefied by that element, whofe known operation in that cafe is to mix all fubftances fo perfectly as to compofe from them a new homogeneous matter? Satisfied, however, that he may elude the conftant effects of his great agent by the imagined compreffion of waters, which in the order of nature could not have refted for a moment on matter in fufion, the author determines that

2

all

all the various ftrata of our prefent lands have been in fufion under the bottom of former feas, and there confolidated by refrigeration.

Meffieurs Raynal and Pallas had imagined a fucceffive change of feas and lands: the one by the perpetual incroachments and derelictions of the ocean, the other by volcanic fires. Dr. Hutton, not fatisfied with these expedients, having conftructed the prefent continents from the decompofition of former lands in the manner we have seen, afferts that nature, which is ever living, and by her perpetual changes of decay and re-conftruction ever renovating this globe, is now preparing under the ocean new fubftances and new lands from the ruins of the prefent. How many millions of years ago our actual habitations were formed under its waters, we may judge from the very flow progress of their decay and the still flower progrefs of their final deposition in the deepest parts of the sea. But to bring together the materials, and mould at will during thoufands of ages the present or future earths, is not the most difficult task of imagination; the most stubborn still remains behind: the means of raising from the deep abyfs these lands, when formed, to their present height above the level of the fea, and to maintain them there when fo uplifted, are not fo obvious. His ready central furnace furnishes him with powers to accomplish the former part. The force of fire and fteam is incalculable, and therefore there is no mass so ponderous which it may not raife to any height (1); but

how

how to preserve it steady for fo many ages in that unnatural elevation, it should seem the doctor has not yet found out. To him I fhall certainly leave it.

In the mean time he will give me leave to examine that process of decay and re-conftruction which certainly takes place on this globe. He maintains that all our prefent lands will one day be washed away into the ocean, which, whilft it overflows that part of the globe which we now inhabit, will raise up new lands from its bofom. To know whether this can ever happen in whatever fucceffion of ages, without a convulfion fuch as we apprehend to have been experienced at the deluge, it will be neceffary to attend to the effects of decay and diluvion which nature presents before our eyes. The fummits of our rocky mountains moulder away, however flowly, and the fame thing happens in a lefs degree to lower eminences. Let us fee what becomes of their broken and shivered ruins. By much the greatest part of them falls at the immediate feet of these crumbling mountains, where it conftructs floping banks extending their dimensions at the expence of their height. These new banks are in time covered with graffes, plants, or wood, defending them in great measure from the attacks of rains, air, and winds; and thereby the bases of perhaps originally upright rocks are both extended and confolidated. By the fame means deep valleys are gradually cumulated. Another part of these spoils is swept away by rains into torrents which take their rife in mountainous tracts.

There

There it in the first place elevates the beds of these torrents, and whatever is not arrefted in them (and that part is very confiderable from the obstruction of larger fragments) is carried by them into larger rivers the beds of thefe are alfo heightened, and no inconfiderable part in every inundation is diffufed over the adjacent plains, elevating their general furface. By the impetuofity of the waters, some part is hurried down to the mouths of rivers, where it raifes fand-banks, and gradually extends the coafts, or forms new iflands, at no great distance from the land. A A very small fhare of the whole is by high tides and tempefts fwept into the deepest parts of the fea, there to fill its cavities, and by a ftill flower progrefs by degrees elevate the general bed of the ocean. Hence its waters too will also at length be raised above their present level. The mouldering fummits of those high cliffs which overhang the fea fall at their feet, and raise their bafes above its waves, and more immediately by fuch incroachments on its limits extend the land. In time, those actual boundaries of its waters will, instead of steep precipices, prefent floping banks, backing and ftrengthening the new lands compofed of the ruins of their former heights (m). Such are the real proceffes and effects of the very gradual decay of our mountains and eminences wherever fituated. Let us now suppose, no matter in what number of ages, all our highest mountains reduced in their height from 3000 to 100 toifes. What will have become of their ruins? At leaft two-thirds will have extended their bafes and raised in a smaller degree all the circumjacent coun

try;