Williams.] FAUNAL DISSECTION OF THE DEVONIAN. 55 
formation as it is exposed along the shores of Caynga Lake in central 
New York. Dr. Cleland accomplished the work successfully. The 
paper which he wrote, containing the results of the investigation, was 
first presented as a thesis for the doctorate degree conferred by Yale 
University in 1900, and was afterwards published as a bulletin of 
the U. S. Geological Survey/' wherein the statistics here used may be 
examined in detail. 
A list was prepared, based upon a very thorough study and dissec- 
tion of the formation from bottom to top. The faunules were collected 
from 70 zones of the 1,224 feet 6 of strata representing the Hamilton 
formation of this region. Upon examination of the collections it 
was decided that, faunally, there were but 25 separate faunal aggre- 
gates represented in the series. These were spoken of in his paper as 
zones, and marked by letters from A to Y. The species were distrib- 
uted quite generally throughout the several zones; but each zone — 
sometimes a few feet thick and occasionally 10 or over 100 feet thick — 
held practically the same faunule from bottom to top; that is, the 
same species in the same relative abundance as compared numerically 
with each other. The investigation was made under my supervision, 
but the identifications were all made by Dr. Cleland, who gave very 
careful attention to the discrimination of the least departure from the 
described characteristics of the species cited. 
In the use of fossils for the purpose of scientifically measuring geo- 
logical time the faunules of such zones as Cleland has analyzed and 
listed may be called bionlc units of the first order; the time repre- 
sented by the continuance of. the particular faunal equilibrium of such 
a unit may be called a Jiemera, applying the term nearly in the original 
sense of Buckman/' but giving it a definition. It may be described 
as the time during which the particular individuals of a given fauna 
and their descendants maintain their faunal equilibrium in relation to 
one another in a local and temporary faunule, as expressed by the 
retention of the same species in the same relative abundance in the 
faunal aggregate. 
The analysis of Dr. Cleland's lists of hemeral faunules and the 
reduction of their statistics to averages gives an approximate concep- 
tion of the constitution of the fauna as a whole, viewed in its relation 
of range through the whole Hamilton formation. It is in reality the 
dominant fauna of the region for the epoch of time through which it 
preserved its integrity as a fauna. 
Table II presents the results of such an analysis. 
« A study of the Hamilton formation of the Cayuga Lake section in central New York, by 
H. F. Cleland: Bull. U. S. Geol. Survey No. 206, 1903. 
''This is Prosser's estimate of thickness. Cleland estimates the total thickness of Hamilton 
to be 1,100 feet (Bull. 206, p. 90). 
<?S. S. Buckman, Quart. Jour. Geol. Soc, November, 1893, Vol. XLIX, p. 481. 
