lOo Ulrich on Correlation of the Lower Silurian. 
acidity of personal biliousness, and the depreciation of the com- 
petency of workers whose language and customs we do not 
understand, should be eliminated. No one man or class of men 
from one or two countries knows enough to propose the best 
plan for thorough mutual assistance. 
Tf the older sciences had been able to avail themselves of this 
plan of mutual help, it is not doubtful that they would be far 
more advanced now than they are. The plain moral is that 
every true scientific geologist the world over should enter into 
hearty sympathy with the work of the Congress, knowing that 
by the cooperation which it secures, the advance of the science 
must be immeasurably greater than it could be from the divided 
energies of a handful of leaders, each using the resources of his 
government to enable him to show that all the rest are hope- 
lessly wrong and himself phenomenally and wholly right. 
A CORRF.LATION OF THE LOWER SILURIAN HORIZONS 
OF TENNESSEE AND OF THE OHIO AND MISSISSIPPI 
VALLEYS WITH THOSE OF NEW YORK AND CANADA. 
BY E. O. UI.RICH, 
As expressed in the above title, the chief purpose of this 
paper is to determine the equivalence of the various beds com- 
prised in the Trenton and Nashville series of Tennessee, those 
of the Trenton limestones of Kentucky, the Cincinnati and 
Hudson horizons of Ohio, Indiana, and Kentucky, and all of 
the beds of Illinois, Iowa, Wisconsin, and Minnesota, included 
between the St. Peter's sandstone and the Niagara limestones, 
with the typical rock sections in Canada and New York. 
Since 1879 I have been gathering data bearing upon questions 
involved in this study, yet I cannot say that I am fully prepared 
to solve any beyond doubt. Whenever possible, T have per- 
sonally visited the typical localities, to either corroborate or 
correct the observations of others. These explorations, how- 
ever, have not been so extensive as was desirable, but when 
combined with the facts gathered by the geological surveys of 
