GEOI;OGY AND PALEONTOLOGY OF THE SCHOHARIE VALLEY 157 



horizon. By far the Luost characteristic and abundant species is 

 Sieberella psendogaleata [fig. 74] , easily distin- 

 guished from S . g a 1 e a t a by its more elongated form and 

 absence of plications. As already stated the upper portions of 

 this limestone are sometimes entirely composed of this species. 

 A number of gastropods occur but they are not abundant. 



Oriskany formation 



Resting on the Becraft limestone or on the darker limestones 

 which in some places succeed the Becraft and represent the Port 

 Ewen beds of the central Hudson region, we find in a great many 

 localities in this district a dark, silicious and very fossiliferous 

 limestone. This is the repiresentative of the Oriskany, which at 

 Oriskany Falls, Oneida co., its type locality, consists of 20 feet 

 of nearly pure, white fossiliferous quartz sandrock. The ro-ck of 

 the Schoharie region appears to be a mixture of quartz and lime 

 sand grains. The latter are commonly dissolved out in the ex- 

 posed rock, which then changes from a dark bluish gray very 

 compact rock, in which the fossils are distinguishable with diffi- 

 culty, to a brown porous sandrock with the fossils represented bj 

 both external and internal molds, which are beautifully preserved 

 and show every detail of marking characteristic of the original 

 which has been dissolved away. The upper member of the forma- 

 tion is a compact quartzite, which forms an even and level floor, 

 marked only by peculiar wave marks, which resemble in a general 

 way the markings found in the Esopus shale next above, and are 

 known by the name of S p i r o p h y t o n (Taonurus) 

 cauda-galli. This upper surface of the Oriskany is so marked 

 that it is readily recognized at a glance. It has been noticed 

 throughout the Helderberg region, retaining its marked surface 

 everj-w^here. From the hardness of this surface layer and the soft- 

 ness of the overlying Esopus shales it follows that erosion is 

 largely concerned with the removal of the overlying soft beds. 

 Thus the Oriskany forms a level platform or terrace wherever the 

 beds are nearly horizontal, a feature which may be observed in a 

 great many places in the Helderberg region. Near Schoharie this 

 may be seen on both West and East hills above the village, the 



