886 The American Naturalist. [October, 
fossils were studied that a definite understanding was reached 
as to the lower limit of the Silurian. These studies were made 
by Barrande in Bohemia. He announced, in 1846, his dis- 
covery of trilobites with peculiar features. To the fauna, as a- 
whole, he gave the name of “ Primordial.” He pointed out 
various differences between it and the English Silurian, call- 
ing this last the “Second fauna.” Barrande did not know at 
this time of Emmons’s name “ Taconic,” nor had he heard of 
the fossils that had been described. Had he known of the 
work of Emmons, he would doubtless have adopted the name 
Taconic, instead of proposing Primordial. 
Continued investigation in North Ameri soon brought 
new facts to light. Owen, in 1847, reported many fossiliferous 
beds in the upper Mississippi Valley that he compared with 
the Potsdam of New York. Roemer found in Texas, in 1848, 
fossils similar to those of Owen; and when Barrande, in 1853, 
heard of and saw the fossils from these two localities, he an- 
nounced that they belonged to his Primordial period. In 1856, 
Prof. W. B. Rogers called the attention of the Boston Society 
of Natural History to the discovery of a trilobite in the slates 
of Braintree, near Boston. He thought it the same species as 
that described in 1834 by Dr. Green as Paradozides harlani, 
and noted, at the same time, the resemblance it bore to a 
species of the genus from Bohemia, called by Barrande, P. 
spinosus. When he sent a photograph of the new specimen to 
Barrande, this authority, too, concluded the two specimens 
were identical. Thus the presence in America of the “ primor- 
dial” fauna of Barrande was at last firmly established, and 
the work to come was the filling in of the outlines, closing the 
gaps and bringing order out of the chaos that had before 
reigned. 
One of the most intricate problems to be settled was that re- 
lating to the age of certain rocks in northern Vermont, occur- 
ring near the town of Georgia. It was in this region that the 
fossils described by Emmons had been found. Their age had 
been variously estimated as Medina, Hudson River and Pots- 
dam (see table of formations on a previous page), but, without 
going into the details of the controversy, it must suffice to say 
