168 
[Assembly 
chard creek. They may be viewed to most advantage on a rock 
forming the floor of a mill, just below the fall at Medina. We 
have seen similar marks very distinctly impressed on a rock pass- 
ing under the Helderberg mountain. 
The most striking feature in these sandstones and shales, is the 
vast abundance of fucoid, or marine plants, particularly that spe- 
cies termed Fucoides Brongniartia by Dr. Harlan. These pene- 
trate every portion of the shale which constitutes the upper por- 
tion of the mass, and upon the surface of the sandstone layers as 
well as of the shales, they project in bold relief, like Gothic 
tracery, although their most delicate transverse striee are seldom 
well preserved, owing to the perishable nature of the strata in 
which they occur. Testaceous remains are seldom found where 
fucoids are numerous, but immediately beneath the strata contain- 
ing them, fresh water and marine shells abound in a limited space. 
This is one of the most ancient fresh water deposites on the globe, 
occurring in the form of three narrow approximate veins filled with 
Cyclosfoma, Planorhis and UnioSj and with marine depositions above 
and beneath them. They seem to have been transported by gentle 
currents to their present site, as the univalves perfectly preserve 
their integrity of form, but the valves of the unios are disunited. 
They occur below the fall in the banks of Oak Orchard creek at 
Medina. Mingled with these, we find a few specimens of Lingu- 
la, which just below are profusely disseminated through the rock, 
and still retaining their pearly testaceous nature, they give to the 
pale greenish sandstone a beautifully variegated appearance, when 
the rock is broken by the hammer, and a fresh surface is exposed. 
Among the fresh water shells we noticed fragments of the marine 
genus Orthocera^ filled with univalves. 
The section of strata over which the cascade at Medina falls, 
presents a fine illustration of the action of contrary currents. All 
the larger layers are variegated with stripes of difierent hue, ob- 
lique to the plane of stratification, dipping at various angles and 
in diflferent strata to opposite points of the compass, similar to 
those we observe in clay and sand deposites of recent formation. 
Other fine sections of variegated sandstone are furnished by the 
Genesee river, north of Rochester, in the vicinity of the two low- 
er falls. The cliffs are perpendicular on both sides of the river, 
and the margin of the water is strewed with immense quantities 
