CHAMPLAIN DIVISION. 
397 
3. Trenton Limestone Group. 
Synonims. Trenton limestone of the Geological Reports of New-York; Metalliferous limerockoi 
Eaton. No. 2 of the Pennsylvania Survey. Cliff limestone of Ohio and Indiana Geological 
Reports. 
Fig. 25. 
1. Isotelus gigas. 2. Strophomena deltoidea. 3. Favosites lycopodites. 
The rocks of this group are limestones and slates alternating with each other; and on the 
Mohawk and Hudson rivers some of the strata abound in fossils which are peculiar in charac¬ 
ter, and distinguish this group from others higher in the geological series. 
The Trenton limestone group thins out from west to east, or is mostly replaced by the 
associated slates, so that it scarcely shows itself in the form of distinct limestone strata con¬ 
taining fossils, in the Mohawk valley east of Schenectady, or in the Hudson valley east of 
Baker’s falls. To the east of the points indicated, the associated and underlying strata are 
exposed in very numerous places; but the Trenton limestone, when seen, exhibits itself in 
alternations of thin layers of black limestone, interstratified with black slate, and destitute of 
the fossils that abound in this rock where it has a greater development. 
The Trenton limestone is generally a dark colored compact or subcrystalline limestone, 
sometimes slaty; in others in strata two to four feet thick, separated by thin layers of black 
shale. Some of the strata are replete with fossil remains, others are nearly destitute of them. 
Some of the thick strata are easily sawed and polished, and make a beautiful black marble ; 
others contain hornstone and chert in small nodules and irregular masses, that render it use¬ 
less for such purposes. 
This rock occupies a small portion of Schenectady county near Amsterdam, on both banks 
of the Mohawk ; thence it ranges northward into Saratoga county ; thence eastward around 
the points of the mountains and along the eastern slope, and enters Warren county at Glens- 
falls and Washington county near Sandyhill. The Trenton limestone is extensively quarried 
