LOWER PALEOZOIC. 211 
sion on the classic ground of eastern New York. The term 
Potsdam, which, on stratigraphic principles, has, in New York, 
a well-characterized upper limit and an easy identification, claims, 
on the paleontological evidence that comes across the country 
from the Northwest, also much of the strata which have been 
known long as Calciferous sandrock. 
10. It is hence obvious that this sub-fauna should not be desig- 
nated from the Potsdam sandstone. 
11. It is equally obvious that the only appropriate designation 
is that of St. Croix, where it was first worked out, and also where 
it was first distinguished as a fauna not appertaining to the Pots- 
dam. 
RfesuMfe OF THE Foregoing Considerations. 
1. It is necessary to choose designations for /mma7 distinctions 
based on dominant types of animal life that have succeeded each 
other with approximate synchronism over large parts of the 
earth. These names will include in their scope large groups of 
strata, and should rank as systemic in the scheme of geologic 
nomenclature, as recommended by the Director of the U. S. 
Geol. Survey. 
2. It is necessary to choose designations for the structural, or 
lithological differences which the rock-masses present. As the 
lithology varies from place to place, the names chosen for these 
lithologic phases must be of lower rank, or serial order, in the 
scheme of nomenclature. 
3. So far as the names chosen by the New York Survey will 
supply those designations, both faunal and structural, they should 
he employed in the system of nomenclature chosen, unless for 
the faunal names some perfect parallelisms were applied at prior 
dates in foreign countries. 
4. Current American opinion requires the use of the term Ta- 
conic for some part or the whole of the strata of the first fauna. 
5. Current American opinion is not in favor of the adoption 
of the European terms Menevian and Ordovician. 
6. The Potsdam sandstone of New York does not contain the 
fauna that Mr. Walcott assigns to the Potsdam sub-fauna ; but 
this fauna is found in the Calciferous sandrock of New York, 
and in the St. Croix beds of the Mississippi valley. The change 
here suggested simply adjusts the nomenclature with the facts. 
