▁entrance ▁of ▁the ▁Ohio ▁River , ▁the ▁Mississippi ▁follows ▁a ▁rock - w alled ▁valley ▁ ▁deep , ▁with ▁a ▁flo od - plain ▁ ▁wide . ▁This ▁valley ▁seems ▁to ▁represent ▁the ▁path ▁of ▁an ▁en larg ed ▁early - g la cial ▁Mississippi , ▁when ▁much ▁precip itation ▁that ▁is ▁today ▁dis charg ed ▁to ▁Hudson ▁Bay ▁and ▁the ▁G ulf ▁of ▁St ▁Lawrence ▁was ▁delivered ▁to ▁the ▁G ulf ▁of ▁Mexico , ▁for ▁the ▁curves ▁of ▁the ▁present ▁river ▁are ▁of ▁distinct ly ▁smaller ▁rad ii ▁than ▁the ▁curves ▁of ▁the ▁valley . ▁Lake ▁P ep in ▁( ▁below ▁St . ▁Paul ), ▁a ▁pictures que ▁expansion ▁of ▁the ▁river ▁across ▁its ▁flo od - plain , ▁is ▁due ▁to ▁the ▁ag grad ation ▁of ▁the ▁valley ▁floor ▁where ▁the ▁Ch ipp ew a ▁River , ▁coming ▁from ▁the ▁n ortheast , ▁brought ▁an ▁over load ▁of ▁fl uv io - g la cial ▁dr ift . ▁Hence , ▁even ▁the ▁father ▁of ▁waters , ▁like ▁so ▁many ▁other ▁rivers ▁in ▁the ▁Northern ▁states , ▁ow es ▁many ▁of ▁its ▁features ▁more ▁or ▁less ▁directly ▁to ▁gla cial ▁action . ▁ ▁The ▁fert ility ▁of ▁the ▁pra i ries ▁is ▁a ▁natural ▁consequence ▁of ▁their ▁origin . ▁During ▁the ▁mechanical ▁transport ation ▁of ▁the ▁till , ▁no ▁veget ation ▁was ▁present ▁to ▁remove ▁the ▁min er als ▁essential ▁to ▁plant ▁growth , ▁as ▁is ▁the ▁case ▁in ▁the ▁so ils ▁of ▁normally ▁weather ed ▁and ▁disse cted ▁pen ep la