HUDSON RIVER GROUP. 
61 
that no line of division, either fossil, mineral or of a stratigraphical character, can be drawn 
between the Silurian and Cambrian systems, as they are presented to us in England. Not 
that there is not a system below the Silurian, for such there must be, from the facts in New- 
York and elsewhere observed; but the subject is there observed by the protean character of 
the Hudson river group, just as we find it to be in the United States, when near the long 
line of the primary, its layers or parts are disturbed as an overlapping rock. 
In Schoharie county, the Hudson group is undisturbed and unaltered, and its maximum 
thickness is not less than seven hundred feet; but from the absence of the succeeding rock, 
its precise position is not made known. Further west in the third district, the whole series is 
complete, and its position well defined. There no mineral line of division exists between the 
Hudson group and the Utica slate beneath, nor the grey sandstone which rests upon the 
group ; but the host of fossils with which the upper part of the group is loaded, totally cease 
with the group ; few or scarcely any of them appear in the grey, and none whatever in the 
redsandstone, the next in succession to the grey. The upper part therefore of the group, 
the sandstone shale of Pulaski, from its well defined fossil character, becomes a good line of 
division to distinguish the Hudson group from the succeeding rocks, and from this circum¬ 
stance is used as a boundary line. 
This group is one of the universal ones. It is the one to which the name of grauwacke 
was originally applied, and when but a few rocks of the class were known. Subsequent 
discoveries of other argillaceous and arenaceous rocks in the same class, each of which 
received the same name, finally created so much confusion as to require that the name should 
be laid aside. 
The two divisions of the group are not coextensive with each other; the lower one enters 
from the first district along the Mohawk, and extends north by Rome through Lewis into 
Jefferson county. The upper division first appears in Oneida county, and from thence west 
and north, is a coassociate of the Frankfort slate, or lower division. The two divisions, as 
in the former reports, will be treated separately, inclining to the opinion that they ought not 
to be put together in local geology. 
Though the Frankfort slate changes by imperceptible gradation from the Utica slate, being 
coassociates, yet a separation would seem obvious from the fact that the dark blue or black 
color of the latter disappears in the usually light color of the former. The Utica slate alternates 
at its lower part with thin beds of dark-colored impure limestone, and is connected by alter¬ 
nation and by organic remains with the Trenton limestone, and presents generally in the 
district a thickness of two hundred feet. The Frankfort slate, on the contrary, alternates with 
a peculiar sandstone to which Professor Eaton gave the name of rubblestone. The slate is 
wholly destitute of calcareous particles, and its great thickness in the first district, though it 
diminishes going west and north, entitles it to a distinct appellation. It is an important rock 
in Europe ; in this State ; in Pennsylvania, and the States to the south. It is the source of 
the springs of Saratoga and Ballston ; the mineral springs from boring, both of Albany and 
Hampton, and the springs at Saltspringville. It is the lowest rock of New-York which con¬ 
tains brine springs, and from which salt, it is said, has been manufactured. 
