28 New York State M\ 



materials is known as sorting. In the case of water, for 

 example, the swifter the current the heavier the material 

 that can be carried. If the force of the water is de- 

 creased for a time finer material may be deposited upon 

 the coarser material, and with increase of current coarser 

 material again follows the finer. This gives a layered or 

 bedded appearance to the deposit. Each layer or bed is 

 known as a stratum (plural strata) ; hence the deposits 

 are known as stratified deposits and the rocks as strati- 

 fied rocks. The different layers may differ in texture of 

 material, in composition of material or in both texture 

 and composition. Where conditions are very uniform 

 there is a very uniform character to the deposits and a 

 lack of bedding. This is true also when the materials 

 supplied have been of a uniform character. Sometimes 

 deposition is too rapid to permit of sorting as in the accu- 

 mulation of talus. In certain glacial deposits, such as till 

 (drumlins and material dropped by the melting of stag- 

 nant glaciers etc.), the transporting agent lacked the 

 power of sorting. Alluvial cone deposits, because of their 

 method of accumulation, show poor bedding; and fluvio- 

 glacial deposits such as kames and eskers rarely show 

 good stratification because of rapid deposition, and slump- 

 ing after the ice has melted away may even have obscured 

 what was there. 



The material composing clastic deposits may be de- 

 rived from preexisting rocks through shattering forces 

 within the earth's crust or through processes acting 

 at the surface. The material derived from disintegra- 

 tion and decomposition may be deposited with little 

 wear to the fragments or the fragments may be so 

 carried about and worn that their appearance is quite 

 altered. By the composition of the sediments the 



