110 CORRELATION OF GEOLOGICAL FAUNAS. [bull. 210. 
of being made up of very thin and even laminae and are very uniform 
for a thickness of several hundred feet. Where they are found in 
the black stage, this uniformity in the size of the grains, the evenness 
of the surfaces of lamination, and the uniformity of the sediments 
from top to bottom are striking characteristics. Faunally they are 
distinguished by a marine fauna containing a few, generally minute, 
invertebrates, many traces of plants, and often the spore cases of 
rhizocarps, together with the bones of large fish, distributed irregu- 
larly among the sediments. These peculiarities indicate quiet condi- 
tions of sedimentation — conditions not enough disturbed by currents 
or even wave action to affect the smoothness of the sediments on the 
bottom — and show that the sources of the sediments were at a con- 
siderable distance. The indications also point strongly to some kind 
of Sargasso sea, as suggested by Newberry; and it is possible that 
this coating of the surface of the sea by a living vegetation may 
account both for the black character of the sediments and for the 
absence of any considerable marine population. 
PORTAGE FORMATION SEDIMENTS. 
The second group of sediments still shows a sparsity of invertebrate 
life, but exhibits alternations of sediments ranging from the fine, 
evenly laminated layers of the black shale to the coarser arenaceous 
shales ami sandstones, with occasional indications of shore action in 
the form of ripple marks, worm tracks, and pebbles. This set of 
sediments is well represented in the typical Portage formation of 
west-central New York. 
FOSSILIFEROUS SHALY SEDIMENTS OF ITHACA GROUP. 
A third class of sediments is found to be typical of the sections 
south of Cayuga Lake, in the formations described by me, a whose 
fauna is more fully elaborated in Mr. Kindle's paper on The Faunas 
of the Ithaca Group. These are composed of alternating sediments 
of sands and shales, richly fossiliferous, much more roughly deposited, 
and rarely showing the peculiar, evenly laminated character of the 
typical Genesee seen in the lighter-colored shales of the Portage of 
the Genesee Valley, and in the Erie shale of Ohio. 
RED SANDSTONE SEDIMENTS. 
The fourth set of sediments is found in the East, and is represented 
by the Oneonta sandstones and the flagstones — purple and red — which 
reach as far west as the Chenango Valley, and traces of which 
appear in the midst of the Ithaca group of the Cayuga Lake meridian. 
These more eastern sediments are generally tinged with red. They 
are often coarse-grained with interspersed pebbles, and sometimes 
a Bulletin U. S. Geol. Survey No. 3. 
