LOWER ROCKS AND GROUPS. 
29 
4. Trenton Limestone. 
This rock usually consists of a dark-colored limestone, intermixed and interlaminated with 
black shaly matter of a character similar to the succeeding rock. It accompanies the Birdseye 
in New-York, generally resting upon it in situations where both appear. In lithological cha¬ 
racters and fossils, they differ essentially ; the latter more particularly distinguish them. It 
appears to be equally extensive with the mass below ; the true distinction between them, 
however, not being always observed. 
Organic Remains. —'Tins is geologically the lowest rock that yields an abundant harvest 
to the pakeontologist. The following are already figured and described : Isotelus gigas, I. 
planus, Bumastis trentonensis, Calymene senaria, Calymene-? Illasnus trentonensis, 
Ceraurus pleurexanthemus, Trinucleus tessellatus, Trocholites ammonius, Inachus undatus, 
Pleurotomaria lenticularis* and three other undescribed species, Subulites elongata, Cyrtoceras 
filosum, Cameroceras trentonensis, Orthoceras multilineatus, 0. trentonensis and three other 
undescribed species, Bellerophon punctifrons, B. bilobatus, B. profundus, Nucula inflata, 
N. faba, Pterinea undata, P. orbicularis, Strophomena alternata, S. deltoidea, S. sericea, 
Orthis striatula, 0. pectinella, 0. leptaenoides, Delthyris expansus, Delthyris-? Atrypa 
extans, A. bisulcata, Favosites lycoperdon. 
5. Utica Slate. 
The Trenton limestone is succeeded by a dark or black carbonaceous slate. Where exten¬ 
sive disturbances have prevailed, this mass is not every where distinguished from the group 
which succeeds, though it merits a distinct place, from its general characters as well as from 
its peculiar fossils. Within the State, it is every where black, and usually soft and fissile ; 
but from contained fossils, it would appear that its color has changed to green in Ohio and 
other places at the west. Thin beds of impure limestone are associated with it in many 
places. From a comparison of specimens from this rock when in the vicinity of hypogene or 
altered masses, it corresponds very closely with the Llandeilo flags of Mr. Murchison; and 
I have detected in specimens of the latter a small Lingula, which is very similar if not iden¬ 
tical with one which occurs in the Utica slate. In its lithological characters, it does not differ 
from the shale interlaminated with the Trenton limestone. 
Organic Remains. — Triarthrus Beckii, Trocholites, Avicula insueta, Nucula poststriata, 
N. scitula, Cypricardia sinuata, Graptolites dentatus, G. scalaris. The following are com¬ 
mon to this rock and the Trenton limestone, according to Mr. Yanuxem : Orthis striatula, 
Strophomena alternata, Lingula ovalis, Favosites lycoperdon, Isotelus gigas, Calymene 
senaria.t 
* The Trochxis lenticularis of the “ Silurian System” ? 
t See Report of Third District. 
