the grand canyon of arizona-第25章

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e；　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　are　both　cut　through；　as　the　plateau　slowly　emerges。　Whether　the　process　of　uplift　is　slow　or　rapid；　as　soon　as　a　stratum　emerges；　it　becomes　subject　to　the　influences　of　weathering；　and　the　uppermost　strata　appearing　first；　they　are　weathered　most。　Hence　the　recession　of　the　uppermost　cliffs　is　greater　than　that　of　the　cliffs　lower　down。　The　differences　in　hardness　and　resistance　to　weathering　are　alone　responsible　for　the　step…like　profile　of　cliffs　and　terraces。　The　lower　platform　owes　its　width　entirely　to　the　rapid　weathering　and　recession　of　the　soft　shales；　which　overlie　the　Tonto　sandstones。　The　red…wall　limestone；　on　the　other　hand；　remains　standing　out　as　a　cliff　because　of　its　exceeding　durability。

The　Faults。　During　the　final　uplift；　the　river　cut　through　the　Cambrian　and　Algonkian　strata；　and　into　the　Granite　Gorge　as　we　find　it　to…day；　and　the　process　is　still　slowly　going　on。　During　these　various　periods　of　uplift；　there　were　other　changes　occurring。　Sometimes　the　uplift　was　uneven；　certain　parts　of　the　plateau　being　lifted　more　rapidly　than　other　parts；　then　occurred　breaks　in　the　strata；　called　faults。　There　are　a　great　number　of　these　faults　in　the　plateau　country；　most　of　them　crossing　the　Canyon　from　north　to　south。　This　faulting；　as　is　readily　seen；　would　produce　cracks；　and　as　the　uneven　uplift　continued；　the　strata　on　one　side　of　the　crack　would　be　lifted　higher　than　the　strata　on　the　other　side。　Or；　the　strata　on　one　side　of　the　crack　would　be　uplifted；　while　the　other　would　subside。

Bright　Angel　Fault。　El　Tovar　rests　directly　upon　the　strata　affected　by　the　Bright　Angel　Fault　line。　On　going　down　the　Bright　Angel　Trail；　one　cannot　fail　to　see；　as　he　passes　the　tap　of　the　cross…bedded　sandstone；　the　break　in　the　strata。　To　the　left　it　is　fully　one　hundred　and　fifty　to　two　hundred　feet　higher　than　it　is　on　the　right。　The　same　depression　may　be　observed　in　driving　out　to　Hopi；　Point；　or　returning。　The　stratum　on　which　the　road　is　made　should　be　at　the　same　level　as　the　stratum　on　which　El