830 PRINCIPLES OF STRATIGRAPHY 



The encroaching sea may finish this surface into an almost abso- 

 lutely level plane of marine planation. In an arid climate a more or 

 less sloping plane (chonoplain) or a series of planes will be formed 

 in the old age of the landscape, these depending for their character, 

 slope, and elevation on the forces controlling the local base level 

 of erosion. 



After the cycle has thus been completed, a new one may be inau- 

 gurated by an uplift of the land or lowering of the sea-level or other 

 base-level of erosion or by a climatic change, etc. Thus a second 

 cycle of erosion will be inaugurated which, if left undisturbed, will 

 continue to its end, and a second peneplain or chonoplain is pro- 

 duced. The cycle may at any time, however, be interrupted by a 

 premature rejuvenation, the earlier cycle remaining thus incomplete. 



Considering the principal land forms resulting from land sculp- 

 ture, we may first note the characteristics of immature stages, and 

 later on those of the completed cycle. Strata unaffected by orogenic 

 disturbances will be considered first, and later on those which have 

 suffered deformation. The types to be discussed include the forms 

 resulting from the normal sculpturing of i. the coastal plain, 2. the 

 monoclinal strata, 3. the dome, 4. the anticline, 5. the basin, and 6. 

 the syncline. Faulted structure (7) will be briefly noted, and after 

 this the peneplain (8) will be considered more at length. 



A. EROSION FEATURES IN UNDISTURBED STRATA. 

 I. The Coastal Plain. 



The submerged deposits on the continental or island margin, of 

 which the sub-coastal plain is composed, represent most typically a 

 series of clastic sediments, in part land-derived and in part thalas- 

 sigenous or derived from organic or biogenic, rarely chemical, de- 

 posits formed in the sea. Stratification is well developed, and the 

 phenomenon of progressive overlap is generally well marked. Re- 

 gressive phenomena, accompanied by landward erosion and seaward 

 retreat of shore features, and transgressive phenomena accompanied 

 by overlap of the upper beds of later formations on the eroded 

 surfaces of earlier ones, are all commonly represented in the struc- 

 ture of the sub-coastal plain. When this is elevated into a coastal 

 plain by epeirogenic movements, or into a mountain by orogenic 

 disturbances, these structures will to a greater or less extent influ- 

 ence the erosion topography induced upon these surfaces. 



The coastal plain has normally a gentle dip seaward, while, close 



