674 ff. S. WILLIAMS 
the chapters of the report, a Division on Correlation, as a distinct 
department of the survey, was organized by the Director of the 
United States Geological Survey. A series of bulletins were 
published (Nos. 80-86), in which a thorough discussion was 
made of the historical development of knowledge, nomenclature, 
and classification of each of the grand systems of the geological 
column on the American continent. The first ‘‘essay’’ was pub- 
lished at the time of the Washington Congress, in 1891. Two 
of the volumes contemplated have not been published at the 
present date. Each of them was prepared by a specialist and 
was based upon thorough study of literature and knowledge of 
the facts. 
In this series of essays, the fact was clearly demonstrated, 
(which had been already announced for the Devonian in the 
American committee’s report ) that the formations of each one 
of the grand geological systems present such great diversity in 
physical features and even in the particular composition of their 
faunas, that two, three, and, in some cases, four distinct classifi- 
cations, with as many sets of different names are needed to repre- 
sent the true state of facts regarding each one as known to sci- 
ence at the present time, in the United States alone. 
The first of this series of bulletins on correlation was issued 
in 1891, at the time of the meeting of the International Congress 
of Geologists at Washington. 
While the European geologists were struggling with the vari- 
ous difficulties arising in the attempt to put the geological feat- 
ures of the various states of Europe onto a single map, with .a 
single system of color conventions and a common legend, the 
United States Geological Survey was dealing with similar prob- 
lems on the continent of North America. Not only was the terri- 
tory covered by the work of the United States Geological Survey 
quite as vast as that covered by the map of Europe (the total area 
of Europe being 3,800,000, and that of the United States being 
3,536,290), but the geology in the several states in America is 
found to present a greater variety of expression and more com- 
plete diversity of composition than is expressed in the states 
