1395.] The First Fauna of the Earth. 883 
None of the rocks of New York are of later age than the 
Devonian. Most of them, indeed, are far older, and so com- 
plete is the series that there is no formation from the Archean 
or metamorphic rocks to the latest Devonian lacking. A por- 
tion of the scheme, as finally adopted, is as follows: 
Lower Sree gs 
Onondag 
Upper Naa 
Silurian } Clinton 
Oneida 
Hudson River 
er | Trenton 
Silurian } Chazy 
Calciferous 
Potsdam 
‘Archean 
All of the formations lying above the Archean are stratified, 
and contain a greater or lesser number of fossils. Each forma- 
tion is generally separated from the one above and below by 
some unconformity, indicating a time during which deposi- 
tion was not going on. These time breaks are also character- 
ized by changes in the organic forms. In other localities than 
New York, these breaks in sedimentation and life do not 
always occur. Sometimes the change in physical features is 
so gradual that it is impossible to say where one group ends 
and the next one begins. Fossils, too, pass from one into the 
other with little or no change. In all such cases there is great 
difficulty in drawing any line of demarkation, but, in general, 
it can be readily done. 
In the early years of the existence of the New York Survey, 
Dr. E. Emmons noted the occurrence of a sandstone in the 
northern part of the State, lying directly upon the metamor- 
phic or igneous rocks. From its proximity to the town of 
Potsdam, he gave it the name of “ Potsdam sandstone.” Its 
position in relation to metamorphic rocks caused it to be con- 
sidered the oldest formation in the State, and the organic re- 
