No. 275.] 
319 
floated upwards with the detritus of the lower rocks, and deposited at 
this era. Similar instances occur in some of the lower rocks; but the 
occurrence of such fossils is not to be considered as characteristic of a 
rock, or as evidence of their existence at the time of its deposition. 
At Hector falls, and above, we find about four hundred feet of this 
group exposed; the lower part contains the ferns of Ithaca; and above, 
some of the other fossils. At this place, we find a few thick layers of 
sandstone, very compact and firm, which have been quarried by Mr. 
Lawrence. Few durable building stones are found in this county, if 
w^e except this sandstone, which however is little used. It furnishes 
the fine flagstones used in Ithaca, and elsewhere. In general characters 
it differs but little from that of the group below; but Fucoides are 
found in greater quantities on the surfaces; many stems of which at- 
tain a diameter of two or three inches. One species, the most abun- 
dant, occurs on the under side of the layers, as if growing on the bot- 
tom of mud and clay, when overwhelmed with the inundation of sand. 
This species is always straight or anastomosing at various angles; some- 
times presenting imperfect reticulations, and at other times, a fancied 
resemblance to a bird's foot. It occurs on many layers, through a con- 
siderable extent, though separated by thick masses of shale. The sur- 
face of most of the layers is smooth, or even glazed with a thin coating 
of shale, which appears to have flowed over it, leaving marks of une- 
qual deposition, and little ridges or prominences where the paste was 
less fluid. The deposition of these shales and sandstones progressed 
slowdy, considerable time having elapsed between the deposition of the 
different layers; and in some instances a lower stratum became partially 
indurated before the succeeding deposit was made. There are nume- 
rous proofs of the general operation, and in particular of the latter, 
where we find, near Jeflferson, the surface of a layer worn smooth and 
grooved, as if by a current, transporting some hard body over it. The 
scratches do not present the roughness of alluvial scratches, but appear 
to have been made before the rock was entirely indurated, or else they 
have been modified by the deposition of shale which succeeded. In this 
instance I have not been able to ascertain the direction of the current, 
though it was probably from the north, and like all other currents in the 
ancient seas, took the direction from the greatest elevations to the 
lowest point 
In some localities the sandstone is replaced by a kind of sandy shale, 
being a mixture of sand and clay; and the whole is rippled, the mark- 
ings affecting each thin layer, and showing that it was deposited from 
