252 PALEOZOIC TIME UPPER SILURIAN. 



South of New York, along the Appalachian region they extend 

 through New Jersey, Pennsylvania, Maryland, and Virginia, in- 

 creasing in thickness, being in all 500 feet or more on the Potomac ; 

 and, as in the North, they diminish westward. 



The subdivisions of the formation observed in the Helderberg 

 Mountains are for the most part undistinguishable out of New 

 York State. The lowest rock, the Water-lime, retains its characters 

 most widely, and has a thickness on the Potomac of 350 feet (Ro- 

 gers). Moreover, in New York it extends west to Ontario co., which 

 is beyond the beds higher in the series. The water-lime is so called 

 because used for making water- (or hydraulic) cement. It is a drab- 

 colored or bluish impure limestone, in thin layers. 



The several New York subdivisions are as follow : — 



5. Upper Pentamerus limestone. 



4. Encrinal limestone. 



3. Catskill or Delthyris shaly limestone. 



2. Pentamerus limestone, 50 feet in the Helderberg Mountains. 



1. Tentaculite and Water-lime group, 150 feet in the Helderberg Mountains. 



An analysis of the Water-lime rock afforded Dr. Beck — Carbonate of lime, 48.4, 

 carbonate of magnesia, 34.3, silica and alumina, 13.85, sesquioxyd of iron, 1.75, 

 moisture and loss, 1.70. One of the beds of the Water-lime strata, consisting of 

 thin clinking layers, abounds in fossils called Tentaculites, and has been named 

 Tentaculite limestone. 



The Pentamerus limestone (No. 2), overlying the Water-lime, is so called from 

 its characteristic fossil, Pentamerus galeatus (fig. 422). It is compact, and 

 mostly in thick layers. The Catskill or Delthyris shaly limestone (No. 3) con- 

 sists of shale and impure thin-bedded limestone, and in many places in New 

 York abounds in the large fossil shell Spirifer macropleurus, and extends as far 

 west as Madison co. It is full of fossils. The Encrinal limestone (No. 4) is 

 confined to the eastern part of the State. The Upper Pentamerus (No. 5), the 

 upper layer, is of limited extent, but has many peculiar fossils : it is named 

 from the Pentamerus pseudo-galeatus (figs. 424, 425). 



The Saliferous beds pass rather gradually into the Water-lime, — their upper 

 layers becoming more and more calcareous, and containing some of the Water- 

 lime fossils. The range of the Salina and Lower Helderberg formations is very 

 different ; for the former is thickest west of the centre of New York, and the 

 latter on its eastern border. 



In the Appalachian region in Pennsylvania the Water-lime group has in the 

 middle belt of the mountains a thickness in some places of 350 feet, while in the 

 southeast belt it is 50 to 200 feet; it thickens to the southwestward. The 

 rest of the Lower Helderberg, consisting also of impure limestones, has a 

 thickness of 100 feet or more in the middle belt, and 200 to 250 in the south- 

 eastern, which thickness is maintained along the Appalachian chain. (Rogers.) 



In the Eastern border region, at Pembroke, Me., in a granitic region, slates and 

 hard sandstones occur with many fossils; at other places in northern Maine, the 

 rock is limestone. In Cutler and Lubec, Me., there is a fossiliferous limestone^ 

 either of this or the Niagara period. (C. H. Hitchcock.) 



