Equivalence and Age of the Formations. 207 . 
equivalent of the Red Sandrock; it is even related in age to 
the Taconic slates; these overlying a western portion of the 
limestone and the quartzyte formation an eastern. If so, the east- 
ern quartzyte formation ts of the age of the later Trenton, or the Cin- 
cinnali group, both in Vermont, Berkshire and Connecticut. 
ill be remembered that the axis of the iron-ore belt is 
and I have 
found that both are unquestionable fossils. The former is the 
shell of a small lamellibranch about six and a half lines long 
and five broad. The so-called Orthoceras is a slender conical 
ge, 
The facts that have been reviewed have established : (1) The 
Lower Silurian age of the limestone series as a whole; (2) the 
unity of position, and of epoch of uplift, of the series; (3) the 
very probable Trenton and Chazy age of the limestone ad- 
joining the whole of the Taconic slate-belt or range; (4) the 
equally probable Upper Trenton or Cincinnati age of the Ta- 
conic rocks. But the age of the more eastern portion of the 
limestone and of the quartzyte and schists remains undeter- 
mined. My opinion is that the quartzyte will be found to be 
newer than the Red Sandrock, and of the same age essentially 
as the Taconic slates. 
[To be continued.] 
