l62 STUDIES FOR STUDENTS 



eflfects of various land reliefs and lithologic characters; second, the 

 influence upon the sediments in the region of deposition, allowing 

 for the various geographic conditions under which the deposit may 

 take place ; third, the relations of climate to transportation by running 

 water. Each of these relations forms a largely independent problem 

 and by the concurrence of evidence from them other factors may be 

 eliminated and a fair degree of certainty attained in regard to the climatic 

 conditions existing during the formation of ancient stream deposits. 



The first part, dealing with the relations of climate to erosion, 

 is necessarily largely physiographic and, in the case of sediments 

 which are carried long distances, is of less final influence than the 

 conditions under which the sediments are deposited and those 

 of the preceding transportation. The purpose of the whole paper 

 is, however, not physiographic but stratigraphic. For this reason 

 it is the relation of physiography to erosion and the consequent 

 supply of sediments which is dwelt upon, rather than the discussion 

 of the land-forms as an end of investigation. Owing to this some- 

 what unusual use of physiography as well as the desire to make the 

 discussion more complete for students in other branches of geology, 

 it is necessary to go over some ground which is familiar to physiog- 

 raphers. Even from a physiographical standpoint, however, it is 

 thought that a brief general discussion of all the climatic factors 

 influencing erosion is not without its value, since it is found to suggest 

 some new points of view upon several old problems. 



For the elaboration of the second and third parts, those upon the 

 relations of climate to terrestrial deposition and the preceding trans- 

 portation, sufficient reason is found in the existence of diverse views 

 held by many working geologists upon the significance of various 

 stratigraphic characters ; and, furthermore, in the general conclusion 

 that climate is a factor comparable to disturbances of the crust or move- 

 ments of the shore line in determining the nature and thfe variations 

 in the stratified rocks of continental or off-shore origin, thus playing 

 a part of large, though but little-appreciated, importance in the making 

 of the stratigraphic record. 



The investigation was instituted to see to what extent profound 

 climatic variations, complicated doubtless with some tectonic move- 

 ments, could account for the great contrasts in the Lower and 



