. Water Supply and Irrigation Papers of the United States Geological Survey . not carrya large amount of gravel. When the Platte is at low stages its bednot uncommonly appears to be paved with cobblestones. These peb-bles and bowlders, on examination, are found to represent a greatvariety of rocks such as are found in the mountains to the doubt when the river flowed at former grades it transported thesematerials and deposited them in terraces. At some places the riverterrace gravels may be seen covering the surface, but usually theyhave been transported by the erosion of sand and clay
. Water Supply and Irrigation Papers of the United States Geological Survey . not carrya large amount of gravel. When the Platte is at low stages its bednot uncommonly appears to be paved with cobblestones. These peb-bles and bowlders, on examination, are found to represent a greatvariety of rocks such as are found in the mountains to the doubt when the river flowed at former grades it transported thesematerials and deposited them in terraces. At some places the riverterrace gravels may be seen covering the surface, but usually theyhave been transported by the erosion of sand and clay and gravita liveaction, so that the terrace feature is obscured. Moreover, there areother gravels which are not unlike them, and it is therefore difficultto distinguish the river gravels as a distinct class of deposits. Stream gravels of local origin.—The conglomerate beds which occurat the base of the Arikaree and locally at higher horizons within thatformation have already been described. The srravels which consti- U. S. GEOLOGICAL SURVEY /ATER-SUPPLY PAPER NO. 70
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