Puslapio vaizdai
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EARTH.

London Publish'd by C Taylor N10 near Castle Street Holborn, Sep '11788.

LECTURE XII.

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HE viciffitudes and changes to which our planet has been fubjected, have very greatly, I might almost say totally, altered its appearance; fo that its original compofition is now to be inferred, and gathered (and sometimes fuppofed alfo) from circumftances which occur but feldom, from facts collected with much care and fedulity, or fought with eagernefs and hazard, wherever fome chafm feems to hint a probability of fhewing nature free from thofe difguifes which are her cuftomary attire. On the furface of our globe, what works, what undertakings, are in perpetual progress; from propofition and commencement, to completion; from completion, to ruin and decay. It is true every animal is by himself diminutive; yet the united, or the fucceffive efforts, of animals, produce no trivial effects in the appearance of their general mother. Some dwell deep in dens, fome burrow fuperficially, fome excavate the very rocks; all while they live, confume part of her productions; when they die, they yield a fomewhat which furnishes fresh productions for fucceffors. What has been the conftant employment of man (especially) during fo many ages? to till the ground; to increase the nobler fpecies of vegetables for his own use, or pleasure, or that of the animals he has fubdued to his fervices: hence barren

heath

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heath has been covered with verdure, cultivation has ferti
lized the very fands ;
fands; hence woods of various natures planted,
hence rivers regulated, hence canals created, hence waters
collected in fome places, drained in others; here he wants
pools, there he forbids marshes; here he deepens a haven,
there he repels the fea, and restrains it by a dyke.-
What a change of the face of nature around fonie opulent
metropolis! the bowels of the earth are ranfacked for riches
or ornament; and what was buried in obscurity, now gleams
in the face of day. These are occurrences fo notorious, so re-
gular, and fo conftant, that to convince ourselves of their
veracity, needs only the ufe of ordinary obfervation.

But there are yet more potent principles, which effect at a ftroke, more than all the fucceffive efforts of mankind, and which, with unabated vigour, with inceffant affiduity, engage punctually in their employment; no change of object, no diverfity of opinion, no attention to other concerns, divert them from their ufual occupation: fuch are the elements we have already treated on, AIR and WATER. Every stream of air which fweeps over the furface of the earth, carries with it much which is not ftrong enough to refift its force: is there a ftraggling atom of earth? it is whirled away, now here, now there; this fpot is deprived of it, that it augments, and trifling as this may appear, the perpetual repetition of it has great effect: producing barrennefs where was fertility, and fertility where was barrennefs. Nor is this all; for the air, by the conftant operation of vapours, fhowers, rains, ftorms, tempefts, performs, by the of agency thefe

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thefe meteors with rapidity, what to itself alone would be tedious. Who has not feen, after a heavy rain, the very furface of the upper grounds conveyed to the lower? evident in ftreams running over its furface, in the difcoloured water of ditches, of brooks, of rivers.-The fame event occurs even on the mountain tops, which by repeated rains are gradually diminifhed. If thefe fcarce-noticed caufes produce in time fuch extraordinary effects, we cannot but attribute yet greater powers to the waters of the fea, whose restless agitation opens or fills, deepens or fhallows, gulphs, bays, havens, ports, wherever it has admiffion. If it is faid, thefe caufes are fuperficial, let us examine beneath their operations,—this is fcarce, if at all poffible, deep as we dig, we find the traces of water and its power the endeavour is hopeless, and rendered more hopeless, when we advert to the operations of earthquakes, of fubterraneous fires, of volcanos, and to many other probable principles, whofe concealment is no impediment to their existence deep in the globe. Under thefe embaraffments, how shall we diftinguish elementary earth? Or is there, or was there ever, one fimple earth, the parent of all others, whofe abundant principles furnished thofe varieties which now perplex us? Rocks are earth, equally with fand or clay; yet the obdurate Alps of granite, feem little allied to the crumbling duft of the fand-pit: and who will fuppofe mines of metals, gold, filver, lead, tin, &c. not to mention falt, coals, flate, and many others, who will suppose thefe to be merely feparations from any original parent? And to which, among thofe we are acquainted with, fhall we at

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XI.

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