4 o LEOPOLD REINECKE 



present is also a factor in the rate of its further development. 

 Moreover, the rate of development decreases so rapidly with 

 decrease of slope that "beveled hills" are probably chronologically 

 closer to forms in early maturity than to peneplains. 



It is proposed in the following section to give proofs for the 

 hypothesis that the rate at which a land surface progresses through 

 the geographic cycle is dependent on its average regional slope, and 

 that its progress becomes slower as the slopes become less. This 

 hypothesis has of course been accepted by physiographers 1 for a 

 long time, and is discussed only because of the emphasis placed 

 in this paper on "average regional slope'' and because the writer 

 has found no presentation of evidence to prove this hypothesis. 



The products of erosion in the normal geographic cycle are 

 practically all removed from the land by streams. The rock waste 

 is moved downstream partly as debris and partly in solution, and, 

 if one could compare the amount of load carried by the streams on 

 any land form during two stages of its progress, when average slopes 

 were known, a measure would be furnished of comparative changes 

 in the rate of erosion as the geographic cycle progresses toward old 

 age. 



The load consists of debris dragged along the stream bed, debris 

 carried in suspension, and rock matter carried in solution, each of 

 which will be considered in the order named. 



A series of experiments have been made by Gilbert 2 on the rela- 

 tions between the load of debris that a stream can drag along its 

 bed, and its slope. 



The experiments proved that the quantity of load dragged 

 by a stream varies in a complex manner with a set of controlling 

 factors — such as slope of stream bed, discharge of water per second, 

 fineness of debris, and form of stream channel. The changes, in 

 amounts carried, vary at a different rate for each of the factors con- 

 cerned. Under the conditions of the laboratory, the load dragged 

 along the stream bed varied with the slope, but at a greater rate. 



X W. M. Davis, "The Peneplain," Am. Geol., XXIII (January-June, 1899), 

 R. S. Tarr, "The Peneplain," ibid., XXI (January-June, 189S), 354, 365. 



2 G. K. Gilbert, "The Transportation of Debris by Running Water," U.S.G.S., 

 Professional Paper No. 86, pp. 10-54, 120, 121. 



