The Andes of southern Peru . aterial. In places, asat the head of the narrows on the valley trail to OUantaytambo,a flood plain has been formed in front of the scarp cut into thealluvium, while the edge of the dissected alluvial fans has beensculptured into erosion forms resembling bad-lands the western side of the valley the alluvial fans are very small,since they are due to purely local accumulations of waste fromthe edge of the plateau. Glaciation has here displaced the effects will long be felt in the disproportionate erosion of thewestern wall of the valley. By far
The Andes of southern Peru . aterial. In places, asat the head of the narrows on the valley trail to OUantaytambo,a flood plain has been formed in front of the scarp cut into thealluvium, while the edge of the dissected alluvial fans has beensculptured into erosion forms resembling bad-lands the western side of the valley the alluvial fans are very small,since they are due to purely local accumulations of waste fromthe edge of the plateau. Glaciation has here displaced the effects will long be felt in the disproportionate erosion of thewestern wall of the valley. By far the most interesting of the deposits of glacial time arethose laid down on the valley floors in the form of an alluvial such deposits havegreater thickness as a rulenear the nourishing mo-raines or bordering allu-vial fans at the lower endsof the valleys, they areeverywhere important inamount, distinctive in topo-graphic form, and of amaz-ingly wide extent. Theyreach far into and possiblyacross the Amazon Fia. 182—Dissected alluvial fans on theborder of tlie Urubamba Valley near HaciendaChinche. A characteristic feature of thevalleys of the Peruvian Andes below the zoneof glaciation but within the limits of its ag-graditional effects. Through alluviation thevalleys and basins of the Andean Cordillera,and vast areas of the great Amazon plains castof it, felt tlie effects of the glacial conditionsof a past age. they form a distinct thoughsmall piedmont fringe along the eastern base of the Andes, andthey are universal throughout the Andean valleys. That a depositof such volume—many times greater than all the material accumu-lated in the form of high-level alluvial fans or terminal moraines—should originate in a tropical land in a region that suffered butlimited Alpine glaciation vastly increases its importance. 272 THE ANDES OF SOUTHERN PERU
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