212 
[Assembly 
mands consideration in an economical point of view, and which also 
presents many points of the highest interest to science. 
The subjoined nomenclature of these rock groups is presented as lo- 
cal, and one of convenience merely, as the divisions are thus easily 
traced. Although there is scarcely a doubt as to what formations in 
Em'ope these are equivalent, yet, I have thought it preferable to de- 
scribe groups of rocks as they are, instead of striving to identify them 
with those of other countries, which must necessarily differ from them 
in some respects. Geological equivalents can be settled in a permanent 
manner, when all the facts of superposition, and the more or less local 
extent of subordinate strata, shall have been definitively ascertained. 
B. FOSSILIFEROUS SERIES OF RoCKS. 
(1.) The lowest in the series is the Hudson River Slate grouj), con- 
sisting of slates, shales, and grits, with interstratified limestones, all of 
which occur under various modifications. This group is overlaid un- 
conformably in many places by the various rock foimations of more re- 
cent origin. 
(2.) The next in order of superposition, in the district under exami- 
nation the past season, is the Shawangunk grits, including the associ- 
ated red and green slates, shales and grits. 
(3.) The next in order is the Helderherg group, which is composed 
of various strata of common and hydraulic limestones of various colours 
and textures, (enclosing a great variety of fossil remains,) interstratified 
Vvdth grits and shales. It includes the hmestones of the Helderberg, of 
Schoharie, Saugerties, Kingston, and the valley of the Delaware and 
Hudson canal to Carpenter's Point, on the Delaware. 
(4.) The Catskill Mountain group terminates the series of indurated 
rocks in the First District. This group consists of white, gray and red 
conglomerates, Avith gray, red, olive, and black grits, slates and shales. 
Some of the strata in the lower half of this group, abound with the im- 
pressions and casts of fossil shells, while those of the upper half con- 
tain the impressions and casts of numerous plants, some of which are 
similar to those of the coal beds of Carbondale. 
The tertiary and alluvial formations complete the series of rocks un- 
der examination this season, in the First District. The groups and for- 
mations will be discussed in order, beginning with the most recent. 
