224 T.S. Hunt on some points in the Geology of Vermont, : 
ada, were found overlapping the Trenton limestone were re- — 
garded as belonging to the Hudson River formation until the — 
study of their fossils led the way to a knowledge of their true 
age and relations. 
The late Dr. Emmons supposed the Red Sandrock to include — 
the Potsdam and Calciferous formations, though he at the same 
time completely misunderstood, as will be shown, its strati- 
graphical relations. Certain trilobites found in this formation 
by Prof. Adams in 1847 were recognized by Prof. Hall as belong- 
ing to the European genus Conocephalus, whose geological hor 
izon was then undetermined, but which was afte shown 
to be a primordial type, and led Mr. Billings in 186], torefer this 
sandrock to the Potsdam formation. (This Journal, II, xxxul, 
232.) Subsequently the Rev. Zadock Thompson discovered it 
the slates of Georgia the trilobites which were by Emmons de 
scribed as Paradowides, but by Prof. Hall were rec aa 
new genus Olenellus, of which he described two species, 0. Ver- 
montana and O. Thompsoni. Notwithstanding its designation, 
the Red Sandrock of Vermont consists in great part of a1 
or mottled granular dolomite associated with beds of fucoidal 
i = intel & 
Len TIMERS ets gt Sn eee TORT TO eae ee 
This formation is well displayed in a section examined by 
les south of 
