GEOLOGY AND PALEONTOLOGY OF THE SCHOHARIE VALLEY 



343 



were due to deposition on a shelving shore the thin edge should 

 be made of the upper beds of the stratum only [fig. 223]. 



When elevation of the peneplain takes place streams naturally 

 become adjusted on the softer strata and so carve out again the 

 cuesta topography by working along the softer beds. This 

 revived topography is not readily distinguishable at first sight 

 from the original cuesta topography. The revived cuestas how- 



Fig-. 222 Thinnino- away of strata by overlap on x-(a, b) and through erosion (peneplena- 

 tion - c-/). In the latter case the lower portion of each bed extends beyond the upper 



ever are much further removed from the old land than were their 

 predecessors. 



That this has been the history of the Helderberg and Schoharie 

 regions seems to be indicated by the correspondence of all the 

 features of the region with those outlined in the theoretic dis- 

 cussion of cuesta development on a coastal plain of the type 

 formed by these old Paleozoic strata. The first cuesta formed 



Fig-. 223 Thinning of strata through overlap on x. Upper portion of each bed extends 



beyond the lower portion 



was probably that of the Oatskill and Oneonta sandstones and 

 the inner lowland between it and the old land was probably at 

 first somewhere north of the present Mohawk valley. As the 

 escarpment Avas pushed southward and westward, lower and 

 lower members of the Paleozoic series were discovered and the 

 cuesta front probably began to take on the terrace form. It must 

 be remembered that the old land at this time formed a semicircle, 

 extending along the north and along the west and southwest. 

 What the original drainage was can of course only be conjee- 



