THE PENEPLAIN 



849 



the coast of Maine, which is still partly above the level of the sea, 

 though the peneplain from which it rises is here completely sub- 

 merged. 



In an old region, where peneplanation has long been in progress, 

 the surface is formed by a layer of atmoclastic material of greater 

 or less depth. With this are mingled peat and other phytogenic 

 material, while here and there may occur a deposit of wind-blown 

 matter. On this surface the rivers will assume a meandering course 

 which has no regard to the underlying structure. When such 



Sectiou across a branching fault. 



Fault and Monocline. 



Fault with tlirown beds flexed upward— a dragged 

 fault. 



Fault with thrown beds lie 



Fig. 223. Erosion scarps formed in horizontal and in ilcxed strata, com- 

 pared with erosion and fault scarps in faulted strata. 



material is exposed to the activities of a slowly encroaching sea, it 

 will be pretty thoroughly sorted and the finer material carried sea- 

 ward to settle in quieter water. But if transgression is rapid, other 

 sediments may be deposited over the ancient soil, which will remain 

 relatively undisturbed. Such ancient buried soils are sometimes met 

 with in the geological series marking former periods of extended 

 peneplanation. 



The Relation of the Peneplain to Sedimentation. A region of 

 low relief will furnish only the finest material for its rivers to 

 carry, and hence the sea bordering a peneplained country will 

 receive only the finest lutaceous sediment which is washed from 

 the lands by the rains and swollen streams. Thus lutaceous sedi- 

 ments, often heavily charged with decaying organic matter, may 

 accumulate in the form of extensive mud flats or deltas. The pres- 



