68 [As 



SEMBLT 



part : these are generally of a drab color, and separated from 

 each other by a thin mass of blue limestone. They are quarried, 

 burnt and ground on a very large scale near Manlius in Onondaga 

 county, and the hydraulic cement of E-osendale and Rondout is 

 probably made from the same beds. (That manufactured at Wil- 

 liamsville, Erie county, is from the upper limestones of the Salt 

 group below ; and in Niagara and Orleans counties, a similar 

 cement is made from some layers of the Niagara group.) 



The fossils of the Waterlime group are but few : the most 

 abundant is the Spirifer pUcata, a little brachiopodous shell 

 which often occurs in great numbers in some grey slaty layers of 

 the rock (Fig. 19, No. 1); Cytherinje, which are shells of a 

 minute crustacean, appearing as smooth black oblong shells, very 

 common in many places (Fig. 19, No. 6) ; and Tentaculites, small 

 conical bodies like spines, ornamented with rings the nature of 

 which is not well understood, though they are believed to be 

 shells once inhabited either by floating marine mollusca, or by 

 marine worms allied to the Serpula (Fig. 19, No. 3). A Lept^na, 

 a thin brachiopodous shell marked with fine radiating lines, is 

 abundant in many localities. 

 • The Waterlime group is succeeded by what are called the 



LOWER HELDERBERG LIMESTONES, 



described in the District reports as the Pentamerus limestone 

 and Catskill shaly limestone, the former mass being the lower : 

 it is a coarse-grained, thick-bedded and often concretionary lime- 

 stone ; while the Catskill limestone is in thin layers, with much 

 shaly or slaty matter interstratified with it. Both of these lime- 

 stones thin out rapidly to the west, and are not recognisable west 

 of Madison county, though at the Helderberg they are eighty or 

 an hundred feet in thickness. They may (with the Waterlime 

 group) be traced through Pennsylvania and Virginia, but are 

 very thin and not found in all places, seeming to be interrupted, 

 and were probably deposited only here and there, in areas of no 

 great extent. 



The fossils of the Lower Helderberg limestones are very nume- 

 rous and interesting, and, with those of the Waterlime group 

 below and the Oriskany sandstone above, fill the third volume of 

 the State Palseontology. A few of the most common and char- 

 acteristic are Rhynchonella ventricosa (Fig. 20), Pentamerus galea- 

 tus (Fig. 21, No. 1), Lepocrinites gebhardi the stem of a crinoid 



