314 BULLETIN OF THE 



The remarkable absence of the Medina-Niagara series of formations 

 between the Hudson River group and the lowest of the overlying lime- 

 stones will be discussed farther on. Here by Catskill nothing was seen 

 that could be surely referred to any of the missing formations ; but 

 Lindsey and Dale describe six or eight feet of Coralline or Encrinal 

 limestone that they identify as some member of the Niagara series. 

 The absence of the Oriskany sandstone is almost as complete. 



The formations observed in our sections of the Little Mountains may 

 be described as follows. 



The Hudson Elver group consists of a great series of fine gray or 

 brown sandstones and shales, with no layers here sufficiently marked to 

 be recognized at their probably repeated outcrops. The layers some- 

 times contain flakes of many-colored clay with the fine sand, implying 

 an erosion near the place of deposition, and some layers have an uneven 

 surface like a mud-flow (see fig. 1). Irregular ripple-marks are common, 

 and in good exposures they may be seen over large surfaces ; but we 

 found no cross-bedding or coarse sandy layers. No fossils were seen : 

 their absence cannot be ascribed to metamorphism, either mechanical or 

 chemical, for many of the strata seem very little altered in spite of the 

 general disturbance. These rocks are well exposed at many points 

 where they crop out above their usual terrace covering of clays and 

 sands that are spread over all the low land ; and are also shown on the 

 creek sections, as on the bank of the Catskill at Catskill Village, where 

 excessive and irregular plications may be seen (fig. 2) ; sharp folds, 

 slickensides, and small faults are very common ; and likely enough 

 faults of larger throw occur, though they cannot be detected. A point 

 of good continuous, and just now of fresh exposure, is in the railroad cut 

 on the bank of the Catskill just below Austin's Mill ; a fine dome-like 

 fold is seen by the stream, and farther on broadly curved surfaces of 

 rippled shales alternating with firm sandstones dip conformably under 

 the limestones (fig. 3). Unconformity might well be expected : the 

 Medina, Clinton, Niagara, and Salina series, about one thousand feet 

 thick in Western New York and over six thousand in Central Pennsyl- 

 vania, are all absent here, unless some few feet of nondescript beds may 

 represent them.* The evidence of conformity and the possible mean- 

 ings of this absence of formations are discussed farther on. 



The beds of passage from Hudson River to Lower Helderberg were 

 best Been on the road leading down to Austin's Mill (fig. 3), and at the 



* If the shaly layers of the Waterlime are considered equivalent to the Salina, 

 this must be a little modified. 



