378 
GEOLOGY OF THE FIRST DISTRICT. 
tainiy that they are of the same geological age ; and not until the last year of the field duties, 
that my colleagues were convinced of its truth. The upturned rocks are so much modified 
in their characters by the causes that have deranged their position, that it requires the strongest 
evidence to convince one that they are no older than the horizontal rocks west of the axis 
of disturbance. These evidences consist in the identification of the same species of fossil 
remains in strata similar in character and in superposition, and in tracing the strata across 
the axis of disturbance. The former can be done in almost every part of the country 
occupied by the Champlain division in the First geological district, by means of the grapto- 
lites, and some other fossils in the Utica slate, and more rarely by fossils, belonging to the 
Trenton limestone. The tracing of the strata across the line of disturbance was satisfactorily 
accomplished only in the valley of the Mohawk. 
Localities where the order of suporposition of the strata of the Hudson-river group may 
be minutely examined, have already been given. Some local detailed sections of these rocks, 
made by Cadet Truman Seymour, one of the assistants, are subjoined. 
Section at the base of the Helderberg mountain, near Salem, Albany county, at what is called the 
MINE.*’ 
Cytherina and Tentaculite limestone. 
Water limestone. 
Slate. 
Grit (calcareous). 
Slate. 
Grit (greywacke). 
Slate, 
Grit. 
Alternations of slate and grit repeated many times. 
Helderberg division... < 
Hudson-river group.... * 
* This name of “ mine” is rather complimentary than just. Some crystals, and particles of iron pyrites are contained 
in a stratum of very impure argillo-siliceous limestone in the Water-lime group of the Helderberg division, about eight feet 
above its base. The stratum is about two feet thick, and geodiferous, containing calcareous spar, like that near Cobleskill 
and Schoharie, that yields fine crystals of calc spar and compounds of baryta and strontia. Some adepts in the use of 
the mmeral rod!! have induced some credulous people to believe that gold, silver and iron, may be obtained at this place. 
