162 
GEOLOGY OF THE FOURTH DISTRICT. 
Under the corniferous limerock of Prof. Eaton were included this rock and the Onondaga 
limestone of the Reports, the latter constituting his “Ceratial rock,” so named from the abun¬ 
dance of Cyathophylli which it contains. The name corniferous is continued as being pecu¬ 
liarly applicable to this rock, though the other limestones contain the same mineral. This 
is the highest limestone of importance in the series, which continues throughout the district. 
In lithological character this rock varies to a considerable degree in its range through the 
district, being at the eastern extremity a fine grained, compact limestone, scarcely presenting 
any crystalline grains. Its color varies from a light greyish blue, to dark blue or black, and 
it is sometimes even of a light grey or drab color. It contains numerous nodules of hornstone, 
and the strata are sometimes separated by irregular layers of the same. In other localities 
these layers of hornstone increase in number and thickness to the almost entire exclusion of 
calcareous matter, and they then present a very harsh outline. Where it possesses this 
character, the calcareous matter is soon dissolved out from weathering, leaving the hornstone 
in jagged and irregular projecting points, from which it receives the local name of “ chawed 
rock.” In the central part of the district the hornstone portions are largely developed, and the 
terminating mass in such situations is a light grey limestone, often of a sub-crystalline texture. 
At the eastern end of the district the hornstone is intermingled and interstratified with the 
calcareous strata, the whole very dark colored. The same character prevails at the western 
extremity of the district, where the rock outcropping on the Niagara has, from its black 
color, given name to the village of Black Rock. 
The rock for the greater part seems to have been composed of finely levigated calcareous 
mud, probably derived from the destruction of corals at distinct points, while at the same 
time siliceous matter often formed no inferior part in its production. The characters which 
distinguish the last rock, viz., the presence of corals and crinoidea are rare in this, and form 
no essential feature. Fossils are generally few, and for the most part consist of shells. 
Some portions it is true, though of small extent, appear as if they may have resulted from 
the destruction of corals. 
This rock is usually distinguished from the limestone below, by its more compact structure, 
the presence of hornstone in layers or nodules, and the absence of Favosites, and crinoidal 
columns, which as before stated always mark the Onondaga limestone where well developed. 
Where free from hornstone this rock furnishes a good building stone, and is readily dressed 
to a smooth face. The darker portions however give a sombre aspect to the structures, and 
the effect upon the eye and the mind is unfavorable. The lighter colored portions, usually of 
the upper part are more suitable for such purposes, and give a good appearance to buildings. 
That portion with much hornstone is only fit for rough walls, for if dressed smoothly, which 
is difficult, it weathers unequally and the moisture finds its way between the nodules of horn¬ 
stone and the surrounding mass, and eventually produces mischief. The upper part of the 
mass is in many places so free from hornstone that it is extensively used for lime burning. 
This rock is interesting to the geologist by its contrast with the preceding, both in color, 
general lithological character and organic contents. It reveals a period when a great change 
