364 STUDIES FOR STUDENTS 



effects, as previously shown, are seen to be largely distinct from those 

 which the topographic conditions alone can produce. The determi- 

 nation of the lithologic characters due to the climatic conditions of 

 erosion and of deposition constitute therefore two more or less inde- 

 pendent lines of evidence as to the climatic conditions of origin. With 

 transportation, however, it is different. Any particular capacity for 

 transportation is conditioned upon topography as well as climate 

 and any change in the size or quantity of the material transported, 

 even if due to climatic change, may conceivably be due also either 

 to a lateral shifting of river currents, if on a small scale, or to some 

 crustal movement if the changes occur on a greater. The proof of 

 the climatic change must, therefore, depend primarily upon the 

 nature of the erosion and deposition, but it will be argued in the 

 course of this article that great climatic changes may result in trans- 

 portative variations of such magnitude that the results become the 

 most pronounced of the three divisions of climatic influence upon 

 fluviatile sedimentation, and have sometimes been ascribed to tec- 

 tonic revolutions. 



For these reasons (because of the dependence of the proof of the 

 climatic change upon the initial and final conditions of sedimentation, 

 and also because of the great importance of such climatic change 

 upon the power of transportation, and the resulting coarseness and 

 thickness of the formation) this middle factor in the conditions 

 governing fluviatile sedimentation is treated the last of the three and 

 not in what at first sight might appear to be its more logical position. 



Effects of Stream Transportation 

 laboratory experiments and laws of river action 

 The effect of transportation upon both the chemical and mechan- 

 ical character of the material has been studied experimentally by 

 Daubree' who found upon submitting fresh and angular fragments 

 of feldspar to prolonged trituration in the presence of distilled water 

 that a very notable degree of decomposition was effected, as was 

 shown by the presence in the water of silicate of potash which rendered 

 the water alkaHne.^ The recent work of Cushman and Hubbard 



1 Geologic experimentale (1879), pp. 248-88. 



2 Op. cit., p. 271. 



