part of this group are not as highly colored as they are in 
the lower part, and they gradually become dark bluish in 
color, closely resembling the lower layers of the Hamil- 
ton Beds, into which they gradate. Indeed, it is often 
difficult to tell the exact line of division between the 
groups. 
The group extends in an unbroken line across the en- 
tire breadth of the county. It is exposed in many of the 
ravines and waterfalls in the towns of Manlius, Pompey, 
Lafayette, Onondaga, Marcellus and Skaneateles. 
The rock attains its maximum thickness in the town of 
Marcellus, where it is about 200 feet thick. The lower 
shales are exposed to the east of the village, while the 
upper layers may be found to the west and south. There 
is a fault in the rock here, and another near Manlius. 
Both are extremely local, however. It is also interesting 
to note, that in the midst of the shale at the latter place 
there is a black limestone, varying in thickness from five 
to ten feet. Itis weathered into huge rough masses, and 
has sometimes been worked and used for rough building 
purposes. It alsomakesan excellent cement. This mass 
of limestone, as well as the concretions of calcareous mat- 
ter, known as septaria, which are found scattered through- 
out the shales of the entire group, clearly indicate that 
the mud of which the group was composed contained 
throughout its mass calcareous material in varying pro- 
portions. Where the amount was small, it congregated 
into the oval masses or septaria; where it was large, as at 
Manlius, limestone was formed. The septaria are oval, 
flattened, or oblong bodies, usually crossed by numerous 
seams, which are filled with foreign matter. They are 
calcareous, and were probably deposited along with the 
material of the shaly matter, the calcareous portion sepa- 
rating from the rest of the mass and uniting. In drying 
and shrinking, these cracks, or septa, were formed. These 
35 
