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SECT. V.

Containing one CHAPTER.

CHA P. XVIII.

Of the Changes on the terraqueous Globe, viz. of Water into Land, or Land into Water.

PROPOSITION I.

To enquire bow much of the Surface of the terraqueous Globe, the Earth and Water feverally take up.

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T is impoffible to know this accurately, because we are ignorant of the Situation of the Earth and Ocean, about the North and South Pole, and because their Superficies are terminated by irregular and crooked Lines, not easily computed or measured. But fo far as we can guefs, from a bare Inspection of the Globe, it feems that the Superficies of the Earth and Water are nearly equal; each taking up half of the Globe's Surface.

PROPOSITION II.

The Surfaces of the Earth and Waters, are not always equally extended, but fometimes more, and sometimes lefs; and what the one lofes the other gains.

THE Sea frequently breaks in upon the Land in feveral Places and overflows it, or waftes it by degrees, and washes it away; by which means

SECT. V. it's Superficies is enlarged according to the bigness of the Plane of Earth it overflows; fuch an Inundation happened of old in Theffaly, &c. But the greatest that we know of have made no fenfible Alteration in the Su face of the Globe, tho' it is poffible that, fome Time or other, there will happen fuch as may; as we fhall fhew in Propofition xviii.

PRO POSITION III.

To compute how much Earth and Water the terraqueous Globe contains.

TO find this accurately there ought to be known exactly the Surface of the Water; and it's Depth in different Parts of the Sea, and also the Bulk of the fubterraneous Waters. All which we are ignorant of, and have no method to find them; and therefore are at a lofs in finding the true quantity of either Earth or Water. We may form an Hypothefis, and take the Superficies of the Water for half the Superficies of the whole Globe, and alfo fuppofe the Sea to be a quarter or half a Mile deep, (one Place with another) not reckoning the Water in fubterraneous Ca

verns.

THESE being granted, the quantity of Water is found thus: Take a quarter or half a Mile from the Semidiameter of the Earth, and find the Solidity of a Sphere, whofe Semidiameter is equal to the Remainder. This Solidity being taken from the Solidity of the whole Globe, half the Remainder is the quantity of Water. This laft being again fubftracted from the Solidity of the Globe, leaves the quantity of Earth, to which, for the Mountains, you must add a fourth or fifth Part of the Bulk of the Water, or even a half: yet

all

all this is but guefs-work, and not to be depended upon for Truth.

PROPOSITION IV.

The Water may leave the Shore, and the Places of the Earth which it covered before, for feveral Reafons; fo that the dry Land may appear where it was Water or Sea before, and a new Plat of Earth may feem to be formed.

TRACTS of Water are feven-fold; 1. The Ocean. 2. Bays. 3. Seas or Streights. 4. Rivers. 5. Lakes. 6. Ponds. 7. Bogs.

THAT Bogs or Marfhes may be drained, either by letting off the Water, or drying it up by continual Fires, or by throwing dry Earth into them, none need doubt; for in feveral Places and Countries there are fertile Fields, where there were formerly nothing but Bogs and Marfhes; as in Weftphalia, Gelderland, Brabant, Holland, Muscovy, &c. So the Peloponnefus in Greece was, in the Time of the Trojans, barren and marshy Ground, but was made fertile in Ariftotle's Time by draining it.

THE fame may be faid of Pools and Ponds, which are not very different.

PROPOSITION V.

Rivers leave their Shores (or part of their Chanels) dry, and form new Parcels of Ground in many Places.

1. IF their Water bring down a great deal of Earth, Sand, and Gravel out of the high Places, and leave it upon the low, in procefs of Time these will become as high as the other, from

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whence

SECT. V. whence the Water flows: Or when they leave this Filth in a certain Place on one fide of the Chanel, it hems in and raises Part of the Chanel which becomes dry Land.

2. IF a River take another Course, made by Art, or Nature, or fome violent Caufe, as the Wind, or an Inundation, it leaves it's former Chanel dry.

3. IF the Fountains that feed a River are obftructed, or cease to send out their Waters, becaufe of the Earth falling in, or by being stopped with Heaps of Sand driven in by the Wind from the adjacent Places, the Chanel of that River becomes dry.

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EXAMPLES of Rivers, whofe Chanels are now dried up either wholly or in Part, are frequently met with among Authors; not of any great Rivers, but of thofe of the fmaller fort, and fome Branches of the great ones; thus that Branch of the Rhine, which formerly run by Leyden into the German Ocean, fome Ages ago forfook it's Chanel, which is now dry Land, and ftagnátes between Leyden and Catwic.

WE have alfo feveral Examples of Shores that have been left dry by Rivers making themselves deeper and narrower Chanels than they used to run in; alfo of Rivers that are not navigable" now, which have been fo formerly, their Chanels being made fhallower, and, in procefs of Time, may be quite choaked up, as the Schelde, &c.. Therefore the Rulers of Countriés take care that the Sand-Banks, Filth, and Sediment, be continually removed out of fuch Rivers, so that they may be kept open and navigable as much as poffible.

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BUT great Rivers are not dried up, or turned into dry Land in a great many Ages, or even Myriads of Ages, because a vaft number of small

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ones flowing from different Parts make up their Waters and feed them; fo that if one or two of them be dried up, or change their Courfe, it will be a long time before fuch an Accident happen to them all. One fingle Sand-Bank indeed might perform Wonders, in choaking up the Paffage of a River, and make it take a new Chanel, whereby the former is dried up; but the River itself continues to flow, because it's Fountains and Branches are not obftructed. Nevertheless it is certain, that neither the Nile, the Tanais, the Elbe, nor the Rhine, &c. did or will always flow in the fame Places, but their Chanels were formerly dry Land, and in future Ages will be so again.

PROPOSITION VI.

Lakes are dried up and turned into Earth.

IF the Lake be fed by Rivers flowing into it, the Change is made by turning the Rivers another Way, or by their ceafing to flow, together with Evaporation. If it receive it's Waters from the Ocean or Sea by fubterraneous Intercourses, these are to be stopped or diverted; and fo the Lake at first is changed into a Fen or Bog, and afterward into dry Ground. Ariftotle (fpeaking of Lakes fed by Rivers) fays, it is certain that the Force of the Water bringing Mud, or fuch likeMatter, into any Lake, changes it into a Fen or Bog, and afterwards into dry Ground; for the Water ftagnating, is in Time dried up. Thus the Mud and Sand, which the many Rivers bring down into the Lake of the Maotis, have made it fo fhallow, that it will not admit fuch large Ships' now, as failed upon it about fixty Years ago.

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