338 NEW YORK STATE MUSEUM 



face stratum and the weakness of the underlying beds. Between 

 the inface of the cuesta and the old land lies the stripped belt, or 

 "inner lowland" which has been opened up by the subsequent 

 streams. The diagrams [fig. 209] show the beginning of the drain- 

 age system on a coastal plain and [fig. 210] the completed simple 

 cuesta. It will be perceived that the inner lowland is widened 

 by the gradual seaward retreat of the inface of the cuesta. By 

 this process the altitude above sea level, of the upper edge of the 



Fig-. 209 Diagram of simple coastal plain after elevation, showing- simple consequent 



drainage 



Fig. 210 Coastal plain after erosion and formation of cuesta topography 



cuesta, gradually diminishes owing to the gentle seaward dip of 

 the strata. At the same time the hight of the inface of the cuesta 

 may increase, for by its seaward retreat lower and lower strata are 

 uncovered, the edges of which become incorporated in the basal 

 portion of the inface of the cuesta. As before stated, if the upper 

 layer is very resistant, while the basal strata are easily eroded, 

 the inface of the cuesta will be steep and rugged. This is essen- 

 tially the case with the front of the Helderberg escarpment at the 

 Indian Ladder, which for purposes of illustration may be com- 

 pared with a normal cuesta front or inface, while the Hudson 

 valley between it and the old land of the Taconic region repre- 



