40 
ous. Other interestng features are its variable thickness, pecul- 
iar fossils, its mineral composition, and its remarkable develop- 
ment of certain forms of marine life, especially the Brachiopods. 
Beginning on the east side of the county at Manlius and pro- 
ceeding nearly westward, there are many exposures of the rock. 
This line of exposure is approximately identical with the strike, 
except in some cases the rock is exposed along the sides of the 
north and south valleys, at points south of the line of strike. (See 
Geological map of Onondaga county, State Geologist’s report, 
1895.) It is always found covered by the Corniferous limestone 
and the points where it occurs are easily located. Its greatest 
thickness is thirty feet, in the southern part of the town of El- 
bridge. ‘The minimum thickness is at the Split Rock quarries, 
where there is only a trace to be seen. The mineralogical com- 
position, color, etc., are given in the descriptions of the different 
outcrops which follow. 
At the quarry one-half mile east of Manlius, the formation 
is eight inches thick. The lower four inches is an imperfectly 
consolidated shale and, perhaps, should be referred to the Helder- 
berg, but as there is a well marked line of division between it 
and the underlying limestone, it seems proper to include it in the 
Oriskany, especially as there are no fossils to determine the mat- 
ter. This part is overlaid by a black concretionary, argillaceous 
sandstone, which is well preserved and full of fossils, mostly in 
the form of casts. 
Rensselaeria ovoides, which is rare at other exposures fur- 
ther west, is plentiful here. Strophomena rhomboidalis, which 
is considered rare for this formation, also occurs here. 
The underlying Helderberg contains corals, besides the 
characteristic species Stromatapora concentrica and Lederditia 
alta. 
The overlying Corniferous limestone is peculiar in that it 
contains great quantities of flint distributed in nodules, which 
are arranged in layers parallel to the stratification. This feature 
of the Corniferous is usually confined to the upper part but in 
this case the flints are nearly in contact with the Oriskany. 
The nodules at this place present a banded structure or alter- 
