302 
Assembly 
A few miles west of Rochester we find interposed between this rock 
and the Geodiferous limestone, a stratum of light gray siliceous lime- 
stone, of a porous and crystalline texture. In some places this rock 
abounds in fragments of encrinital columns, which are perfectly crystal- 
line, and stand out in relief where the other portions of the rock have 
been removed by the action of the weather. This is the same rock 
which at Lockport furnishes the fine building stone so extensively used 
in that vicinity. The greatest thickness of this stratum within the li- 
mits of our district does not exceed thirty feet. 
SECTION V. 
Geodiferous and Bituminous Limestone 
The shale and limestone last described are succeeded by the Geodi- 
ferous limerock" of Prof. Eaton. This limestone is well characterized at 
Lockport and at Niagara falls: farther east it loses the geodiferous cha- 
racter, and diminishes in thickness. The rock is regularly stratified, 
compact, of a gray, bluish gray or brownish gray colour. It is suflScient- 
ly distinguished from all other limestones by its finely granular texture, 
presenting on fracture numerous shining points: the lustre is vitreous, 
or resinous. The resinous lustre is produced by bitumen, which colours 
the small crystalline laminae. The most striking feature of this rock, in 
the localities referred to, is the numerous cavities, or geodes, many of 
them filled with anhydrous gypsum, or lined with crystallized limestone 
or fluer spar. The beautiful specimens of dogtooth and rhomb spar, with 
sulphate of strontian and selenite from Lockport and Niagara falls, are 
from cavities in this rock. Blende also occurs in the cavities with the 
minerals mentioned. Many of these cavities present some partially de- 
cayed organic body. In some places the structure of the rock is very 
irregular, presenting curved, contorted and concentric laminas, as if the 
mass had been disturbed when partially indurated. The whole of this 
rock is bituminous, particularly the upper portions; the odor is perceiv- 
ed on percussion. 
At the Niagara falls there are about eighty feet of this rock disclosed; 
the lower portions are gray, becoming darker, and containing more and 
larger geodes as we ascend. At the top of the falls it is of a brownish 
gray colour and resinous lustre, containing blende disseminated and in 
geodes. Above this, there is a thickness of about one hundred feet, 
which is less geodiferous, and inclining to a bluish color. The upper- 
* Though both these terms are applicable to the rock under consideration, the same charac- 
ters are also possessed by the carboniferous limestone at Black Rock. 
