CLIMATE AND TERRESTRIAL DEPOSITS 263 



flooded condition of the swamp areas leads to the preservation of 

 carbonaceous strata. 



With the accentuation of climates toward aridity or toward a 

 cool and continuously pluvial condition, these chemical and organic 

 deposits, developed most typically on the distal margin of the delta 

 spread inland and become of greater geological importance, as illus- 

 trated by the brine pools of the desert delta of the Volga, on the one 

 hand, or the impenetrable flooded jungles of the Amazonian silvas, 

 on the other. 



Climatic Influences in Regions of Deposition , 



The geographic and climatic influences in the regions of erosion 

 produce two effects in the region of deposition. One, a chemical and 

 mineralogical influence which becomes generalized and vague with 

 prolonged transportation; the other through variations in erosion 

 causing variations in the coarseness and quantity of waste, also becom- 

 ing masked by the effects of long transportation. On piedmont slopes 

 therefore, being nearer the headwaters, the climatic conditions of 

 erosion, of transportation, and of deposition all find obvious expres- 

 sion ; but over the more distant parts of a river system the more con- 

 spicuous factors governing the nature of the sedimentation are the 

 variable nature of the transportation, regulating the coarseness and 

 quantity of the waste, and the variable climatic conditions existing 

 in the region of deposition, largely governing the chemical and mineral 

 nature of the deposit. The microscope and the chemical analysis 

 will still, however, be able to trace underlying influences due to the 

 nature of erosion, as indicated by existing deposits of loess in Missis- 

 sippi and red laterite muds spread in places upon the bottoms of tropical 

 seas. 



In taking up in detail the present topic of the influence of climate 

 in regions of deposition, the effects upon the deposits of four kinds 

 of climates may be considered, namely, constantly rainy, intermittently 

 rainy, subarid, and arid. The effects of iacreased cold, by preventing 

 evaporation, produce results similar to an increased and more con- 

 tinuous rainfall. Cool summers rather than cold winters are more 

 effective in this way and lead in northwestern Europe to the production 

 of extensive peat deposits in regions which receive but twenty-five to 



