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Thesamepartsoftheeartharenotalwaysmoistordry，buttheychangeaccordingasriverscomeintoexistenceanddryup。Andsotherelationoflandtoseachangestooandaplacedoesnotalwaysremainlandorseathroughoutalltime，butwheretherewasdrylandtherecomestobesea，andwherethereisnowsea，thereonedaycomestobedryland。Butwemustsupposethesechangestofollowsomeorderandcycle。Theprincipleandcauseofthesechangesisthattheinterioroftheearthgrowsanddecays，likethebodiesofplantsandanimals。Onlyinthecaseoftheselattertheprocessdoesnotgoonbyparts，buteachofthemnecessarilygrowsordecaysasawhole，whereasitdoesgoonbypartsinthecaseoftheearth。Herethecausesarecoldandheat，whichincreaseanddiminishonaccountofthesunanditscourse。Itisowingtothemthatthepartsoftheearthcometohaveadifferentcharacter，thatsomepartsremainmoistforacertaintime，andthendryupandgrowold，whileotherpartsintheirturnarefilledwithlifeandmoisture。Nowwhenplacesbecomedrierthespringsnecessarilygiveout，andwhenthishappenstheriversfirstdecreaseinsizeandthenfinallybecomedry;andwhenriverschangeanddisappearinonepartandcomeintoexistencecorrespondinglyinanother，theseamustneedsbeaffected。
Iftheseawasoncepushedoutbyriversandencroacheduponthelandanywhere，itnecessarilyleavesthatplacedrywhenitrecedes;
again，ifthedrylandhasencroachedontheseaatallbyaprocessofsiltingsetupbytheriverswhenattheirfull，thetimemustcomewhenthisplacewillbefloodedagain。
Butthewholevitalprocessoftheearthtakesplacesograduallyandinperiodsoftimewhicharesoimmensecomparedwiththelengthofourlife，thatthesechangesarenotobserved，andbeforetheircoursecanberecordedfrombeginningtoendwholenationsperishandaredestroyed。Ofsuchdestructionsthemostutterandsuddenareduetowars;butpestilenceorfaminecausethemtoo。Famines，again，areeithersuddenandsevereorelsegradual。Inthelattercasethedisappearanceofanationisnotnoticedbecausesomeleavethecountrywhileothersremain;andthisgoesonuntilthelandisunabletomaintainanyinhabitantsatall。Soalongperiodoftimeislikelytoelapsefromthefirstdeparturetothelast，andnooneremembersandthelapseoftimedestroysallrecordevenbeforethelastinhabitantshavedisappeared。Inthesamewayanationmustbesupposedtoloseaccountofthetimewhenitfirstsettledinalandthatwaschangingfromamarshyandwaterystateandbecomingdry。