388 Johnston — Imbricated Structure in River-gravels. 



stream and dip downstream. This view is apparently 

 incorrect. The stones finally assnme a position in which 

 they offer the least possible resistance to the current. 

 If the stones dipped downstream they would present 

 their edges to the current and therefore offer consider- 

 able resistance to the current. Moreover field observa- 

 tions show that the dip is upstream. It is well recog- 

 nized that in hydraulic work it is necessary, in order to 

 achieve maximum results, to direct the stream against the 



Fig. 1. 



Fig. 1. — Vertical section of river gravels at Campbellford, Ontario, Can- 

 ada, showing imbricated structure. The direction of the current was from 

 right to left. 



"stratification" of the stones, that is in a direction oppo- 

 site to that of the current which deposited the stones. 

 Imbricated structure is frequently used by placer miners 

 as a criterion to determine the direction in which the 

 streams in abandoned channels flowed and thus to 

 attempt to trace the old channels. The inclined attitude 

 of the stones is chiefly relied upon for this purpose and 

 the further fact that the longer axes of the stones usually 

 lie in the direction of the current. Imbricated structure 



