afew counties besides our own. For this reason it is not 
always mentioned in works on geology as one of the divis- 
ions of the Hamilton Period. 
Neither is its thickness as great as that of some of the 
limestone formations already mentioned. Its average 
thickness is not more than fifteen feet. The greatest 
thickness in our county, however, is considerably more 
than this, it being thirty feet thick in the ravine a mile 
northwest of Spafford Corners. 
It is an impure, fine-grained limestone, with a dark 
blue color when freshly broken, which on long exposure 
to the weather becomes lighter colored. It is often accre- 
tionary in structure, breaking into small irregular frag- 
ments. The layers on separating sometimes show the 
fibrous appearance which was so common in the Lower 
Helderberg Period. 
Among the fossils found in this group are two hand- 
some species, which are wholly peculiar toit They are 
the Rhynchonella venustula and the Orthis Tulliensts. 
Since these fossils have never been found in any other 
group, by their presence alone we can readily distinguish 
the Tully Limestone from any other. 
The formation occurs sparingly in the towns of Fabius, 
Tully, Otisco, Spafford and Skaneateles. Some of the 
best places for studying it are: Tinker’s Falls in Fabius; 
just south of Delphi; Ousby’s farm, south of Tully; one 
mile south of Vesper; in the northeastern part of the town 
of Otisco, which is the most northern point where it oc- 
curs; one mile south of Borodino; and in any of the ravines 
near the head of Skaneateles Lake. 
At Tinker’s Falls the limestone is some fifteen feet in 
thickness. It forms a sort of shelf over which the water 
falls, and as the shale (Hamilton) which occurs below the 
limestone is more rapidly disintegrated by the atmospheric 
agencies than is the limestone, we have a natural cave ex. 
44 
