CLIMATE AND TERRESTRIAL DEPOSITS 383 



generation, of the importance of repeated epeirogenic and orogenic 

 movements in maintaining the land surface and supplying, through 

 subaerial erosion and fiuviatile transportation, the materials of the 

 sedimentary rocks, has led to the recognition of the tectonic causes of 

 many of the changes whicli distinguish and separate the series of sedi- 

 mentary formations. But it is probable that tectonic causes have been 

 too freely ascribed in explanation of the origin of formation differences 

 in so far as a possible climatic origin has not been held in mind. An 

 inspection of geological literature indicates that, although the possi- 

 bility of such climatic causes has been increasingly appreciated in 

 recent years by certain investigators, yet in general, geologists have not 

 considered the possible effects of climatic changes when seeking the 

 causes of variations in strata, especially such as are due to size of par- 

 ticles. Usually the climatic factor is only regarded when considering 

 the characteristics of the fossil fauna and flora or when deposits are 

 present of such obvious nature as those of salt and gypsum or the 

 products of glacial action. It is desired here to call attention to cli- 

 matic change as a cause of sedimentary variation in detrital deposits 

 of co-ordinate importance with marine planation and crustal move- 

 ment. In order to discriminate correctly between the three classes of 

 deposits where occurring in the geologic record criteria must be 

 employed for their separation, though it is doubtless true that a correct 

 evaluation of the factors entering into the formation of many deposits 

 may never be achieved. 



It is natural that the influence of climatic change in producing 

 shiftings of the sedimentary facies should be the last kind of action to 

 reach a true appreciation. Marine and tectonic conglomerates and 

 sandstones are now observed in the making, but the shifting of these 

 regions of deposition through climatic changes and by which climatic 

 deposits as distinct from the others are to be determined is only evident 

 on comparing the present relations of erosion and deposition with 

 those occurring in the recent past under the same tectonic but different 

 climatic conditions. 



In conclusion something may be said of the relations of the three 

 classes of deposits to each other. The geologic environment of a land 

 consists of three fundamental factors : the relations of land and sea, the 

 relations of topography, and the relations of climate. Each of these 

 may be practically stable for a time, being subject to minor oscillations 



