618 PROCEEDINGS OF THE NEW YORK MEETING 



stratigraphic. For this reason it is the relation of pliysiography to erosion 

 and 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 physiographers. Even from a physio- 

 graphical 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 fluviatile deposition and the preceding transportation, sufficient 

 reason is found in the existence of the diverse views held by many working 

 geologists upon the significance of various stratigraphic characters, and, 

 furthermore, in the general conclusion of the present paper, that climate is a 

 factor comparable to disturbances of the crust or movements of the shoreline in 

 determining the nature and the variations in the stratified rocks of continental 

 or offshore 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 movements, could account 

 for the great contrasts in the Lower and Upper Carbonifei'ous formations of 

 eastern Pennsylvania — formations which had been found by the writer from 

 observations in the field to be continental in nature, and therefore their con- 

 trasted features not to be attributed to changes in the relations of land and 

 sea. 



An abstract of the body of the paper is as follows : 



Part I. Relation of Sediments to Regions of Erosion 



Observations of the nature of river sediment show tliat it is only in local 

 deposits that the character is markedly due to the kind of rocks undergoing 

 erosion, so that in regions where the sediment has no relation to the adjacent 

 formations but little difficulty will be found in allowing for the more or less 

 unlinown lithological nature of the source. 



The interrelations of topography and climate to erosion are more complicated, 

 l)ut it is shown from present instances that even where land relief leads to 

 vigorous erosion the influence of arid or humid climates is able to make itself 

 felt in the ratio of coarse to fine material and the freshness or degree of 

 decomposition of the fine. In the mature stage of the topographic cycle these 

 differences become accentuated. The influence of old topography is of less 

 importance, since under such conditions fluviatile continental deposits are 

 reduced to a minimum. Between the climatic extremes, however, the results, 

 as are well known, are still conspicuous, leached claj-s being the mark of 

 rainy and loess and dune sand of arid climates. 



Under the relations of temperature to erosion, the influences of vegetation, 

 of frost action, of snow action, and of insolation are discussed. It is noted, 

 as Chamberlin and Salisbury have pointed out. that increased cold tends to 

 weaken the power which vegetation possesses in producing decay but prevent- 

 ing erosion. Increased frost action is found to greatly increase the rate of 



