386 
GEOLOGY OF THE SECOND DISTRICT. 
are no falls or uplifts of any magnitude, the whole thickness is nowhere exposed, unless at 
and below Brownville. Here it is slightly broken and elevated by an uplift, giving the mass 
a dip to the northeast and southwest, and forming an indistinct anticlinal axis. The force 
producing this uplift, elevated the whole mass higher upon the south than upon the north side. 
Just below Brownville, the drab colored layers belonging to the birdseye appear; and in one 
of the strata, I found the orthis which is so abundant at Chazy in the same position. In one 
of the strata above, cytherinse in large individuals are not uncommon. 
Isle La Motte Marble. 
Resting upon the birdseye at the base of the cliffs at Watertown, is a mass of black lime¬ 
stone about eight feet thick. It is remarkably thick-bedded; in fact it appears to be one 
stratum, the divisional planes being exceedingly obscure. This is the same wherever this 
rock occurs. At Isle La Motte, where it is about twelve feet thick, it has been blasted 
through as if it were one continuous stratum. 
At Watertown, this rock is broken, or seems to be formed of lumpy masses; such at least 
is the case wherever it has been exposed in the banks of the river, and in this respect it differs 
from the same rock at Glen’s-Falls and Isle La Motte. It is black, fine grained, without 
shaly matter, but is disposed to break into irregular masses, and hence it appears unsuitable 
for the purposes for which it is so valuable at other places. It is here called the Seven-foot 
tier, and is quarried for walls, and a variety of purposes of a coarser description. 
The character of this mass connects it rather with the birdseye than with the trenton lime¬ 
stone, between which two it lies. I have never observed the fossils of the trenton in it; but 
a columnaria, and one or two species of large orthoceratites occur in it. The combined facts 
in relation to this mass seem to indicate that it is the terminating mass of the limestones below 
the trenton, or that it is not the commencement of that order of things which succeed and 
follow in the latter rock. From its compactness, we find the fossils difficult to procure, and 
none of them in a state fit for illustration by figures, except the columnaria which has already 
been placed before the reader (p. 276, Fig. 73, No. 2). 
The value of this stratum at other places in the Second district, encourages me to hope, 
that in the vicinity of Watertown, it may be found in a state suitable for marble. It forms 
for an inconsiderable extent the surface rock; it merely crops out beneath the trenton, with¬ 
out extending beyond it. The caves of Watertown appear to have been excavated in this 
mass, and they were probably formed at the same period as were all the other surface excava¬ 
tions. At a few points, the removal of this rock has caused the trenton to cave in, and form 
upon the surface depressions more or less conical. 
