160 HELDERBERG DIVISION. 



better answered by considering the whole mass above the plaster beds, up to the Penta- 

 nierus limestone, as one division, we have disregarded the former grouping in this respect. 



I propose describing the superior division, as it exists in different parts of the State ; as 

 this, like several other groups or sub-groups, exhibits many important variations in the 

 composition of the individual strata. 



Valley of the Rondout in Ulster county. The best, or perhaps the most interesting expo- 

 sure, is at the High falls. The series at this place stands thus in tlie ascending order : 



1. Oneida conglomerate; or, as it would be called here, the Shawangunk grit of Mr. Mather. 



■2. Thin-bedded red and green shales below impure thin-bedded limestones ; above, similar in form 

 and structure to the Manlius waterlimcs. The inferior part contains many irregular-shaped 

 geodes lined with crystals of lime, and the brown and red masses contain many implanted crystals 

 of sulphuret of iron : some of these crystals are liable to decompose. 



3. A grayish white grit, ten feet thick. It resembles the grits of the Clinton group in Herkimer 



county ; but it will be understood that this remarkable mass, in this position, is above this group, 

 and hence is not an equivalent of it at this place, but is an intercalated portion. 



4. Thick irregular-bedded cherty limestone, geodjferous in some parts : it is dark-colored. It is pro- 



bably the pentamerus in part blended with the delthyris shaly limestone, as some portions are 

 drab-colored and shaly. The thick dark-colored layers are quarried for cement. 



The falls of the Rondout are produced by an uplift, in which the entire series enumerated 

 above are broken three times (See Plate XX. Section 3) . 



One remarkable fact is worthy of notice in the valley of the Rondout. Near Rosendale, 

 the Hudson-river series supports and is in connection with the shaly limestones I have just 

 noticed ; so also the same relations prevail near Catskill, and at Becraft's mountain. At 

 the falls of the Rondout, however, the Oneida conglomerate is in connection with the 

 Waterlime series. It is possible that the series described as the waterlimes may be a 

 disguised form of the Clinton group, and the limestones referred to the pentamerus and 

 delthyris would then become equivalents with the Niagara grouj). A fact which supports 

 this view, is the existence of the Catcnipora cscaroides. Sufficient lime could not be 

 taken to settle the question in regard to the true character of these rocks. At the time 

 they were examined, they were considered as the waterlimes, and equivalent to those of 

 Onondaga county ; and it is in this light that they have been regarded thus far in this 

 report. 



If the red mottled shale is equivalent in part to the Clinton group, it is wanting in the 

 characters by which this series is known in Oneida and Herkimer counties. The fucoids are 

 absent, and the limestone beds replace the grits which abound in the counties just cited. 

 Tiie decomposing green shales, with cavities lined with crystals of calc spar, resemble 

 very closely a mass which lies just above the village of Manlius, and which is there soon 

 succeeded by a thin band of the Pentamerus limestone. These remarks will prevent in a 

 great measure the inculcation of error, as they will serve to put the student in the track of 

 inquiry when visiting the valley of the Rondout. Mr. Mather regards a part of the series 

 here as belonging to the Clinton group. In whatever light, however, we may regard this 



