CLIMATE AND TERRESTRIAL DEPOSITS 381 



after the exclusion of the possibiHty of a tectonic origin, the syn- 

 chronous relations of erosion and deposition are investigated for the 

 three portions of the river system and the relative location of portions 

 undergoing degradation and aggradation are determined. Even by 

 those who have recognized the frequent climatic origin of changes in 

 river grade the necessity of clearly stating these relations seems to 

 have escaped attention. 



CLIMATIC CHANGES DUE CHIEFLY TO TEMPERATURE 



In the discussion of the relations of climate to erosion the char- 

 acteristics of weathering in hot and cold cHmates were discussed. 

 Under the present topic of the relations of climate to transportation 

 it need only be said that a cooler climate, by producing less evapora- 

 tion, will alone serve to increase the percentage run-off of the river 

 systems. A change from a temperate to a rigorous climate tends, there- 

 fore, not only to increase the amount of waste given to the river in its 

 upper portion, but will result to some extent in an increase of the 

 coarseness and quantity of material carried through to the delta. A 

 change from a temperate to a hot cHmate on the other hand will^tend 

 to diminish the percentage of run-off, and with it the coarseness of the 

 waste which is transported. Provided that the waste becomes finer, 

 however, from greater decomposition, the quantity carried by the 

 stream may not be decreased. At' the headwaters the amount of 

 waste is presumably increased by more intense insolation or more 

 rapid decomposition over the conditions of a milder climate, tending 

 to build piedmont slopes. '"■ '^^ 



Oscillations to climatic extremes of any sort may, therefore, be 

 considered to accelerate rock destruction, but only oscillations toward 

 a more concentrated or voluminous rainfall or toward marked cool- 

 ness of cHmate will result over the regions of distant deltas and epicon- 

 tinental seas, in an increased quantity or coarseness of deposit. 



Conclusion 



conglomerates and sandstones of marine, tectonic, and 

 climatic origin 



Summing up the preceding discussion it is to be concluded that 

 conglomerates and sandstone formations intercalated between others 

 of different nature may be due to three distinct causes : 



