GEOLOGY OF THE FOURTH DISTRICT. 
same neighborhood. In some places in the western part of Wayne county, it diminishes and 
nearly disappears, and again continues of variable thickness. On the Genesee river it is twenty- 
three feet thick ; farther west, at Medina, it is about three feet; while at Lockport it is 
scarcely visible, or intermixed with the terminal mass of the Medina sandstone. Again, on 
the Niagara river it has a thickness of four feet. Wherever seen it exhibits its predominating 
character, as a soft green argillaceous shale, splitting into thin laminae, and crumbling rapidly 
on exposure. 
At Sodus, and other places in Wayne county, where this rock is well exposed, it contains 
thin wedge-form layers of limestone of small extent, which are fossiliferous as well as the 
shale itself, containing large numbers of crinoidal joints, and fragments of drifted shells and 
corals, as well as perfect specimens. These are sometimes replaced by carbonate of iron, 
and the substitution is so entire that the crystalline structure is as perfectly preserved as in 
those of carbonate of lime. 
On the Genesee river, the mass is a pure argillaceous shale, entirely free from any calca¬ 
reous intermixture, and contains no fossils. At this place, it forms a distinct green band in 
the river bank at the lower falls; and between this and the middle falls is seen both in the 
bed and banks of the stream. Below the falls, it forms the same distinct band for a mile or 
two farther north, and is well exhibited in the road leading from the brow of the hill to the 
steamboat landing. On exposure it crumbles rapidly into thin minute fragments, and in wet 
weather forms a tenacious greenish mud. 
2. Oolitic or Lenticular Iron Ore. 
Argillaceous iron ore of Eaton, including the lenticular and jaspery varieties. Lenticular clay iron 
ore of Dr. Beck. Fossiliferous iron ore of the Pennsylvania Survey. 
Succeeding the green shale upon the Genesee river, is a thin bed of iron ore ; this is not 
present in all situations, its place being sometimes marked by the slightly ferruginous color 
of the upper part of the shale, or lower part of the limestone above. The quantity of the 
material seems to have been very small, and from its nature widely diffused; it probably 
existed in the menstruum, which at the same time held in suspension the materials forming 
the other associated deposits. In some instances, it has forced its way through all the upper 
deposits and rests on the lower shale, and in other cases the upper shale has arrested its pro¬ 
gress. It appears to have been intermingled with both the limestones, and probably separated 
from them by its greater specific gravity, falling to the bottom, where the shaly matter had 
become too firm for its farther descent. 
The purple or brownish band which marks the lower green shale at Sodus point, while the 
iron ore is there absent, and again, the fossils of that division replaced by carbonate of iron, 
sufficiently prove the intimate mixture and diffusion of the ferruginous matter through the 
whole. 
In the town of Ontario, Wayne county, this bed of ore attains its greatest thickness, which 
