90 NEW YORK STATE MUSEUM 



dermining of the upper layers thus results in their ultimate breaking 

 down from non-support, and the resulting fall of rocks may be of 

 a dangerous character. Care is therefore necessary in the examina- 

 tion of these sections, and the warnings of the section guards should 

 always be heeded. These men patrol the tracks continually from 

 early morning till after the last train has passed at night. This is 

 necessary, as the fall of rocks is continuous, and often of such 

 amount as to obstruct traffic for some time. Any one who will 

 watch these clififs for a time from one of the projecting points where 

 a comprehensive view may be obtained, and note the almost in- 

 cessant fall of rock particles, will receive an impressive object lesson 

 in the processes by which cliff retreat is effected. 



In many cases the shale banks are covered with a coating of red 

 mud carried by rains from the red soil above them. This creates 

 the impression that the color of these lower shales is red like that 

 of the shales higher up in the series, and only after breaking off 

 fresh particles can the true color be seen. 



2 These gray shales are succeeded by sandstones and sandy 

 shales, some of the former massive, quartzose and in beds 6 or 7 

 inches in thickness, separated by shaly layers. The sandstone is 

 gray and often porous, as if it had undergone some internal solu- 

 tion, which suggests that fossils may have been present which were 

 dissolved by percolating waters. Fragments of fossils are occasion- 

 ally found, but mostly in an unidentifiable condition. Many of the 

 thinner and more clayey beds have raised markings on their under 

 side, which may be indicative of the former presence of seaweeds in 

 the muddy beds of this period. Small black phosphatic pebbles, 

 often very smooth, are not uncommon in some of the layers, and 

 larger masses of black, apparently carbonaceous shale are occasion- 

 ally found mixed with the sand. In the gray shaly sandstone beds 

 the Medina gastropods and bivalves (pelecypods) occur sparingly, 

 and usually in a poor state of preservation. Some of the thin layers 

 are calcareous, though still containing a large proportion of argil- 

 laceous matter. These are generally fossiliferous, the most common 

 organism being a small cylindric bryozoan.^ Fragments of these 



^ Identified provisionally as Helopora fragilis (fig. 74). 



