the grand canyon of arizona-第18章

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visions　of　the　eras。　In　the　Proterozoic；　there　are　two　periods；　viz。：　the　Archaean　and　the　Algonkian。　The　Paleozoic　has　six　periods；　viz。：　the　Cambrian；　Ordovician；　Silurian；　Devonian；　Carboniferous　and　Permian。　The　Mesozoic　era　has　three　periods；　the　Triassic；　Jurassic　and　Cretaceous；　while　the　Cenozoic　era　names　five　periods；the　Eocene；　Oligocene；　Miocene；　Pliocene　and　Pleistocene。

Absence　of　Certain　Strata。　To　shorten　our　story；　let　me　at　once　say　that　during　the　periods　that　the　Ordovician；　the　Silurian　and　the　Devonian　were　forming；　the　Grand　Canyon　region　was　either　above　water　so　that　it　received　none　of　these　sediments；　or；　if　any　were　deposited；　they　were　almost　entirely　removed　by　the　weathering　processes　before　described；　ere　the　region　again　sank　into　the　ocean　to　receive　the　deposits　of　the　Carboniferous　epoch。

The　Carboniferous。　During　this　latter　period；　more　than　three　thousand　feet　of　strata　were　deposited。　These　are　the　most　striking　in　appearance　of　all　the　Canyon　strata；　for　they　reach　from　the　Tonto　shales　to　the　rim；　and　consist　of　three　principal　strata　（with　many　smaller　ones　in　between）。　The　largest　is　the　red…wall　limestone；　which　constitutes　the　base　of　nearly　all　the　architectural　forms　found　in　the　Canyon；　and　is　the　thickest　of　all　the　　strata。　It　presents　the　〃tallest〃　wall　of　the　series。　The　two　separate　walls；　one　above　the　other；　on　the　top　of　the　Canyon；　as　seen　in　the　arms　of　the　amphitheatre　at　El　Tovar；　are　the　other　two　wide　members　of　this　Carboniferous　period。　The　lower　is　the　cross…bedded　sandstone；　and　the　upper　the　cherty　limestone。　There　is　a　remarkable　difference　in　the　appearance　and　the　material　of　which　these　Carboniferous　strata　are　formed；　and　those　of　the　East　and　Europe。　We　generally　think　of　coal…bedscarbon　when　this　period　is　mentioned。　Here　there　are　none。　In　the　East；　in　England；　and　in　other　parts　of　Europe；　vast　marshes　existed　in　this　period；　and　the　rank　vegetation　of　these　marshy　areas　formed　the　coal…beds；　with　which　the　Carboniferous　there　abounds。　It　is　only　by　the　fossils　found　that　the　periods　to　which　the　various　strata　belong　are　determined；　and　the　fossils；　millions　of　which　abound　in　the　upper　limestone；　are　clearly　of　the　Carboniferous　epoch。

As　these　strata　and　this　period　bring　us　to　the　〃rim〃　of　the　Canyon；　it　might　be　easy　to　imagine　that　the　processes　of　uplift　and　subsidence；　and　deposition　of　more　strata；　as　far　as　the　Canyon　region　is　concerned；　now　cease。　Such；　however；　is　not　the　case。

Later　Strata。　As　we　go　away　from　the　Canyon；　either　north　or　east；　we　find　thousands　of　feet　more　of　the　later　depositions；　and　the　geologists　affirm　that　many　of　these　at　one　time　may　have　overlaid　the　Canyon　region。　There　is　circumstantial　evidence；　amounting　almost　to　proof；　and　Figure　3　of　plate　facing　page　99　suggests　what　that　evidence　is。　It　should　be　carefully　noted　that　the　Canyon　has　been　cut　through　the　highest　portions　of　a　ridge；　which　runs　generally　from　east　to　west；　and　the　slopes　of　which；　therefore；　were　north　and　south　from　the　ridge。　As　one　travels　north　from　the　Canyon；　he　finds　all　the　way　along；　for　hundreds　of　miles；　that　he　goes　on　a　down　slope　for　a　number　of　miles　and　then　suddenly　comes　to　the　jutting　edges　of　slightly　tilted　strata　（only　2　degrees）　which　make　a　cliff　up　which　he　must　climb。　Arrived　at　the　top　of　this；　the　downward　descent　begins　again；　until　another　ridge　of　these　slightly　tilted　strata　appears；　see　Figure　3　of　plate　facing　page　99。　Thus　he　continues　up　into　Utah；　and　south　and　east　into　Arizona。

Now；　in　imagination；　restore　these　cliffs　of　Permian；　Triassic；　Jurassic　and　even　Cretaceous　strata　over　the　whole　Canyon　platform。　Figure　4　of　plate　facing　page　99。

Red　Butte；　which　is　the　prominent　landmark　seen　from　the　railway　on　the　right；　when　going　from　Williams　to　the　Canyon；　is　said　to　be　a　remnant　of　the　Permian。

Deposition　of　Strata　in　Shallow　Water。　It　is；　I　believe；　generally　accepted　by　the　geologists　that　the　accumulation　of　much　of　the　sediments　of　the　Cambrian；　Carboniferous；　Permian；　Triassic；　Jurassic　and　Cretaceous　periods　took　place　in　shallow　water；　and　that　the　sea　bottom　slowly　sank　under　the　weight　of　the　increasing　deposits。　Hundreds；　thousands　of　years　must　have　elapsed　during　the　process；　for　the　indications　are　that　the　sinking　did　not　exceed　a　few　inches　every　hundred　years！　As　carefully　measured；　these　sediments　then　amounted　to　about　two　miles。　Imagine；　then；　these　Cambrian　rocks；　that　at　El　Tovar　are　clearly　seen　above　the　〃granite〃　or　Archaean；　sunk　in　the　ocean；　to　the　depth　of　two　miles；　and　covered　over　with　the　various　strata；　the　topmost　of　which　was　barely　above　sea　level　at　periods　of　low　tide。

Cretaceous　Uplift。　Then　began　another　epoch　of　uplift。　Slowly　the　Cretaceous　rocks　emerged　from　the　sea；　and　were　subject　to　the　fierce　attacks　of　nature　that　produce　erosion。　Now　we　have　to　grope　blindly　for　a　while；　as　the　wise　ones　do　not　have　facts　enough　upon　which　to　speak　with　definite　certainty。　But　it　is　assumed　that　a　great　warping　of　the　earth's　crust　took　place；　and　that　in　this　revolution　some　of　the　plateau　sank；supposedly　the　northern　part；　though　it　certainly　extended　across　the　Canyon　nearly　as　far　south　as　Williams　and　Ash　Fork；　and　other　partsthe　edgesarose；　and　thus　formed　a　basin　which　became　another　vast　inland　sea。

Eocene　Lake。　We　know　this　was　an　inland　sea；　and　had　no　connection　with　the　ocean；　for　all　the　fossils　and　sediments　deposited　in　it　reveal　that　they　are　fresh…water　organisms。　In　this　sea；　as　in　the　earlier　oceans；　vast　deposits　of　sediment　were　made　in　the　early　Eocene　period；　and　another　period　of　subsidence　occurred。　Then　the　great　lake　was　drained；　and　the　uplift　began；　slow　and　sure；　then；　and　not　before；　were　the　conditions　existent　that　have　made　the　Canyon　country　as　we　see　it　to…day。　Peaks　and　islets　received　the　rainfall；　tiny　rivers　were　formed　that　grew　larger　and　cut　their　way　in　deeper；　as　the　uplift　continued。　The　principal　stream；　which　was　then　born；　was　the　Colorado。　It　is　supposed；　from　various　evidences；　that　the　rainfall　was　very　much　more　abundant　then　than　now；　and　consequently　the　rivers　had　greater　flow；　and　more　eroding　and　carrying　capacity。　The　uplift　continued；　and　the　geologists　tell　us　it　did　not　cease　until　about　fifteen　thousand　feet；　deposited　since　Cretaceous　times；　were　thrust　up　into　the　air。　As　almost　all　this　mass　of　deposition　has　disappeared　from　the　immediate　Canyon　region；　we　are　compelled　to　believe　that　it　has　been　swept　away　down　the　Colorado　River　to　join　the　sands　of　the　Carboniferous　and　later　periods　in　the　Colorado　Desert；　the　Salton　Basin；　the　great　low　region　of　Lower　California；　and　the　Gulf　itself。

Less　by　Erosion　in　the　Canyon　Region。　Now　figure　out　for　a　few　moments　the　results　of　these　different　erosive　periods。　Eleven　thousand　five　hundred　feet　of　Algonkian　gone；　a　small　amount　of　erosion　in　the　Cambrian　epoch；　the　depth　of　which　is　unknown；　and　then　the　great　denudation　of　the　Eocene　period　sweeping　away　upwards　of　fifteen　thousand　feet　of　strata；　give　us　a　total　of　twenty…six　thousand　five　hundred　feet　that　have　totally　disappeared　from　the　Canyon　region。　A　vertical　mile　is　five　thousand　two　hundred　and　eighty　feet。　Mount　Washington　is　about　six　thousand　five　hundred　feet　above　the　sea；a　trifle　higher　than　Mount　Lowe；　near　Pasadena；　California。　Take　off　from　this　six　thousand　five　hundred　feet；　say　one　thousand　five　hundred　feet；　for　the　level　of　the　country　at　the　base　of　these　two　mountains；　and　then　imagine　a　region　five　times　as　high　as　both　of　them；　covering　an　area　of　country　of　possibly　thirteen　thousand　to　fifteen　thousand　square　miles；　slowly　planed　off　by　the　erosive　forces　of　nature。

Formation　of　River　Beds。　How　was　it　done？　I　have　spoken　of　the　peaks　and　islets　that　first　emerged　from　the　Eocene　Sea；　and　received　the　rains。　Down　their　slopes　ran　the　earliest　watercourses；　first　as　rills；　then　as　creeks；　finally　as　rivers。　The　higher　the　peaks　ascended；　the　more　the　accompanying　land　was　lifted　up；　and　therefore　the　longer　and　deeper　became　the　rivers。　The　course　of　a　river　once　established；　it　is　exceedingly　difficult　to　change　ithence　the　law　that　geologists　call　〃the　persistence　of　rivers。〃　By　and　by；　the　uplifted　country　appeared　as　one　vast　area　of　river　valleys；　separated　by　stretches　of　plateau。　Little　by　little；　working　by　laws　that　are　pretty　well　understood；　the　swift　flowing　avers　cut　downwards。　When　their　velocity　ceased；　the　widening　of　the　river　courses　began；　and　progressed　with　greater　rapidity；　so　that；　in　time；　the　divides　that　intervened　between　the　rivers　were　worn　away；a　process　rudely　shown　in　Fig。　5　A。　B。　C。　and　D。　of　plate　on　page　110。

The　Formation　of　the　Canyon。　Now；　in　imagination；　let　us　hark　back　to　the　day　when　this　plateau　was　in　the　condition　thus　described。　Nearly　everything　in　the　way　of　strata　has　been　planed　down　to　the　Carboniferous　rocks。　The　plateau　is　about　at　sea　level。　One　great　river　already　exists；　with　two　arms；　now　called　the　Green　and　the　Grand；　the　main　river　some　day　to　be　known　as　the　Colorado。　Slowly　the　uplift　begins。　It　is　a　fairly　even　process；　and　yet　there　is　slightly　more　pressure　brought　to　bear　under　the　southern　portion；　so　that　the　whole　mass　has　a　slight　tilt　to　the　north。　Professor　Salisbury　found　certain　beds　of　rock　at　seven　thousand　eight　hundred　feet　above　sea　level　at　the　base　of　the　San　Francisco　Mountains　near　Flagstaff。　Forty…five　miles　north；　at　the　Grand　Canyon；　these　same　beds　are　only　six　thousand　four　hundred　feet　above　sea　level；　while　at　the　Vermilion　Cliffs；　another　forty…five　miles　to　the　north；　they　are　but　four　thousand　four　hundred　feet　above　the　sea。

Yet　in　spite　of　this　northward　tilt；　when　the　eye　ranges　over　the　country　to　the　south　and　west；　from　the　upper　porch　of　El　Tovar；　a　large　area　of　depression　can　clearly　be　seen；　showing　that　surface　erosion　has　planed　away　much　of　the　upper　crust。

The　Plateau　Region。　Now　we　are　ready　to　take　a　look　at　the　borders　of　the　plateau　region。　On　the　north；　it　extends　into　Utah；　where　still　higher　plateaus　bound　it。　To　the　west；　it　extends　by　gigantic　steps　into　the　desert　region。　The　main　step　is　along　the　Grand　Wash；　near　the　one　hundred　and　fourteenth　meridian。　To　the　south；　there　is　one　glorious　step；　known　as　the　Mogollon　Escarpment　（locally　the　Red　Rock　Country）；　some　three　thousand　feet　high；　which　extends　for　a　number　of　miles　east　and　west；　and　then　breaks　down。　This　step　and　broken　levels　lead　to　the　irregular　lands　of　Central　and　Southern　Arizona。　On　the　east；　the　plateau　extends　to　the　Echo　Cliffs　beyond　Marble　Canyon；　and　as　far　as　the　ridge　of　the　Continental　Divide；　where　the　Santa　Fe　crosses　the　Zuni　Mountains；　east　of　Gallup；　N。　M。

Present　Conditions。　With　this　general　view　of　the　great　plateau　in　our　mind's　eye；　we　are　prepared　to　examine　present　conditions　at　any　given　spot　in　the　Canyon。　Let　us；　therefore；　take　a　seat　at　El　Tovar；　and　try　to　read　a　few　pages　of　the　stone　book　of　Creation　as　opened　there。　Suppose　all　this　vast　region　at　about　sea　level；　and　the　uplift　just　beginning。　The　course　of　the　Colorado　River　is　already　well　defined。　As　the　uplift　continues；　the　cherty　limestone　and　possibly　the　cross…bedded　sandstone　ar