The New York Series. — Clarke and Schuchert. 1 15 
It will be observed that the classification proposed by the 
four geologists was wholly stratigraphic. It did not purpose to 
express the time units or groups thereof except so far as such, a 
subdivision of the strata must of itself imply a corresponding 
division of time. Nor did the geologists contemplate any uni- 
form grouping of their units in terms intermediate between 
their major and minor divisions. 
It has, however, come to pass that such a grouping of the 
early New York units has found its way into quite general use. 
Such terms as Niagara group, Hamilton group, Chemung 
group, are current expressions in contemporaneous writings 
and they are not employed at all in the sense in which they 
were sometimes used by Vanuxem and Hall. This fact is well 
known and it is generally recognized by all students con- 
cerned with the stratigraphy of the early formations, that this 
condition has come about indirectly through the influence of 
the important summaries of American geology published by 
the late professor J. D. Dana (Manual of Geology, four edi- 
tions). In presenting the succession of paleozoic events these 
works have treated the subject as history must be treated, as 
a succession of time units. These units, which have been 
termed epochs, were grouped together into periods, and each 
period was given the name of the most conspicuous, widely 
distributed or otherwise best characterized of its epochs. Thus 
have arisen terms for secondary divisions in the paleozoic his- 
tory of New York which duplicate names that must remain 
permanently in use for time units and their stratigraphic equiv- 
alents. The duplicating terms thus introduced into New York 
history are the following: Trenton, Niagara, Onondaga. 
Corniferous, Hamilton, Chemung. The distinguished author 
to whom reference has been made never employed these terms 
in any other than a chronologic sense; the present frequent ap- 
plication of them with a stratigraphic meaning of precisely the 
same scope as the time divisions, is a perfectly natural and le- 
gitimate outcoipe. This practice has, however, not only 
caused confusion from duplication within the boundaries of the 
state, but it has led to much embarrassment in the correlation 
of the stratigraphic succession of other states with that of New- 
York. The point has doubtless been reached when these terms, 
