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THE GEOLOGICAL HISTORY OF NEW YORK STATE 55 
their own. Fossil seaweeds, but not animal remains, are common 
in the Oneida-Medina beds. Various fossils exist in profusion in 
the Clinton and Niagara formations, while in the middle Salina 
beds fossils are altogether absent because the water of that time 
was intensely saline. The waterlime beds at the base and top of 
the Salina are usually poor in fossils except for the remarkable 
assemblage of organic remains known as eurypterids which be- 
longed to the arachnid class but are now wholly extinct. Fossils 
are generally rather common in the uppermost Siluric beds of the 
State. 
DEVONIC AND CARBONIC PERIODS 
The Devonic history of New York State is comparatively simple 
and the records are remarkably well shown in rocks of that age. 
Devonic strata comprise the whole Catskill and Southwestern 
plateau provinces, except for a few small patches of Carbonic rocks, 
and thus cover more than one-third of the area of the State. They 
are more widespread on the surface than the rocks of any other age. 
The combined thickness of the Devonic strata is over 4000 feet, 
which is considerably more than for any other Paleozoic period in 
the State. ; 
That the Devonic strata, on the Hudson valley side, formerly 
extended some miles farther eastward than they now do is proved 
by the presence of small outliers of Devonic rock, for example, 
Becraft mountain just southeast of Hudson, the Rensselaer grit 
- farther north and the Skunnemunk mountain southwest of New- 
burgh. During part of the time the Devonic sea, or arms of it, 
reached as far east as these outlying masses and doubtless far be- 
yond over the regions of Massachusetts and the Connecticut valley. 
The bold outcropping edges of thick Devonic strata facing the Mo- 
hawk valley and, in the Helderberg escarpment, the Ontario plain, 
make it certain that the strata formerly extended some distance 
farther northward. It is more than likely that this northward ex- 
tension of Devonic rocks was not beyond the southern border of 
the Adirondacks; at least we have no positive knowledge that the 
Devonic sea ever covered any of northern New York (see figure 
18). 
There was no disturbance of any kind at the close of the Siluric, 
so that period passed very quietly into the Devonic. The Oriskany 
sandstone was for many years regarded as the base of the Devonic 
but now, as a result of a careful study of the fossils, the line be- 
tween Siluric and Devonic is drawn just below the Helderberg lime- 
