109 



A Topographic Result of the Alluvial Cone, 



By a. H. Purdue. 



An alluvial cone that is eoniro>ed mainly of more or less finely com- 

 minuted material would not last loni;- enough after the area covered by it 

 ceases to be one of deposition to produce an enduring topographic feature. 

 It would soon succumb to the agents of erosion and transportation. Even 

 if composed of coarse material, its life might be short if the lithological 

 character and climatic conditions were such as to bring rapid disintegra- 

 tion. But if tlie cone be composed mainly of coarse material that can 

 withstand the weathering agencies, there is every reason to believe that it 

 would have lasting topographic residts. 



In transverse section, alluvial ccuies are higher in the middle than on 

 the borders next the escarpment, as shown in Fig. 1, so that the tendency 



is for the streams which form them to shift either to the right or to the 

 left, running along the base of the escarpment. If such a stream is not 

 overloaded at this point, it becomes a cutting stream, and the profile, that 



shown in Fig. 2. Should the cone be formed immediately below the .iunc- 

 tion of two streams, as in Fig 3, both streams might shift, one to either 



