CLASSIFICATION OF STRATIFIED ROCKS 675 
of Europe altogether. So that the members of the United States 
Geological Survey, in their own legitimate work, have been 
obliged to consider as wide problems as have engaged the Inter- 
national Congress of Geologists, whose preponderating majority 
is made up of European members. 
As early as 1881 a cartographic system was devised by the 
survey for the preparation of its maps. This was described in 
the second annual report of the survey and also was communi- 
cated to the Second International Congress meeting at Bologna 
in 1881. As happened to similar schemes presented by repre- 
sentatives of the various Europeans, this was a provisional 
scheme whose modification was the natural result of their com- 
parison at the meetings of the congress, and the trials of the 
system in actual mapping of widely diverse problems. 
In the years 1889-90 the importance of a uniform and estab- 
lished scheme for all the maps of the United States led to the 
holding of a ‘‘Conference on Map Publication,” which was called 
by the Director of the Survey, was composed of nineteen of the 
most experienced and ablest geologists of the country, and was 
held in Washington, in January 1889, 
As a result of this conference a scheme of classification and 
set of rules for use in mapping the results of the work of the 
United States Geological Survey were prepared. These rules 
were published in the Tenth Annual Report in 1889, and have 
been the basis upon which the reports and maps of the survey 
have been constructed since then. The scheme differs from the 
European scheme adopted by the International Congress in many 
particulars. The difference which is most striking on com- 
paring the two, has relation to the principle of uniformity itself. 
The European system is built on the assumption that uniformity 
in nomenclature is practicable, and should be attained as far as 
consistent with the divergent opinions and practices of the vari- 
ous states concerned. The United States system is fundamen- 
tally elastic, and rests on the general assumption that uniformity 
is practicable only in respect to the grander divisions, and that 
diversity in both naming and classifying the subdivisions of 
