Introduction — Principles Involved. 



formations or to another, or whether it found lodgment at some 

 time intermediate between the three principal stages of deposi- 

 tion. This is true especially of isolated remnants of one or 

 another of these formations. 



The preceding hypothetical cases may be changed to illustrate 

 another phase of the relations of the several members of the 

 series. Let it be supposed that the original plain of depositiok 

 covered by formation I, sloped to the sea. Erosion of its sur- 

 face by drainage direct to the sea, after its attitude was so 

 changed as to favor erosion, might result in deposition along the 

 shore. The new sediments would be left somewhat as shown by 

 2. in Fia- 



D> 



the materials of 2 being derived from the higher 



Fig. 5 



Fig. 6 



parts of 1. If this process were repeated, the result would be 

 illustrated by Fig. 6, where a third formation overlies the sea- 



