CLIMATE AND TERRESTRIAL DEPOSITS 619 



disintegration in young or mature topography without correspondingly increas- 

 ing the powers of waste-removal. The Gila conglomerate of Arizona is dis- 

 cussed as an example of a great conglomerate formation resulting primarily 

 from a climatic change in which the ratio of erosion to transportation had been 

 increased through increased frost action at times of glaciation in other regions. 

 Increased snoicfall works in an opposite direction, by protecting the surface 

 from disintegration and promoting transportation. 



Under the effects of climatic changes resulting in an increase of temperature. 

 it is pointed out that in regions of topographic relief insolation is a weaker 

 force than frost action. In all geologic times, irrespective of climatic varia- 

 tions, it has worked most strongly in the torrid and has been practicall.y absent 

 from the polar zones. In intensity it must have varied considerably, owing 

 largely to geographic as well as possibly to solar conditions. In regions of 

 humid climate rock decay takes the place of insolation and also operates most 

 strongly in the torrid zone : but on account of the mat of vegetation it is not 

 Ivnown if erosion is weaker or more rapid than in a temperate climate. 



In conclusion, it is pointed out that an examination of the matrix of fluvia- 

 tile conglomerates is of importance for separating the climatic from the 

 topographic conditions of origin, while the simultaneous development of con- 

 glomerates within many hydrographic basins, as Davis has shown, may point 

 to a climatic as against a tectonic origin. Finally the relative rates of erosion 

 under various climates are discussed and it is concluded that the development 

 of plains of marine denudation depends largely on the climatic factor, taking 

 place most readily in an arid climate. As a result of the discussion of the first 

 part, it is concluded that climatic variation is a major factor, comparing with 

 subordinate tectonic movements, in governing both the kind and quantity of 

 the material supplied to the rivers. 



Part II. RELATioisr of Sediments to Regions of Deposition 



In the second part, the influence of topography is first considered, the 

 piedmont slopes being notably better drained than deltas and only covered 

 with carbonaceous deposits in a cool and rainy climate. Over the delta there 

 is a progressive flattening of the grade with the production of swamp areas, 

 to some extent even in desert climates. A number of factors independent 

 of the climate, such as the building of two confluent deltas or a slowly rising 

 water level, tend to increase the area of swamp ; but in desert climates there 

 is a close association of the swamp deposits with sharply contrasted evap- 

 oration and jTeolian products. Under all climates the amount of swamp area 

 reaches a maximum on the seaward margin of the delta. Following this 

 preliminary discussion, the effects of five kinds of climates are consid- 

 ered : constantly rainy, arctic, intermittently rainy, semiarid, and arid. Each 

 impresses well marked distinctions upon the flood-plain deposits. The con- 

 stantly rainy gives rise to carbonaceous and well leached clays and sands, 

 besides beds of peat; the arctic climate differs in the less leached clays, con- 

 taining especially more potash; in intermittently rainy climates the carbona- 

 ceous deposits of the flood-plains are local, the materials are oxidized during 

 seasons of dryness, the clays are slightly calcareous, and fossils are apt to be 

 scanty. It is concluded that such deposits occur to an unappreciated extent in 



