Regulation of Nomenclature. — Gilbert. 139 
plan, and in the elaboration of that plan a certain amount of 
uniformity in the use of terms was imperative. The rules of 
nomenclature and classification published in 1890, in the Tenth 
Annual Report of the Survey, were notably conservative, em- 
bodying the minimum of regulation consistent with the orderly 
progress of geologic mapping and map publication. As the 
areal work progressed and geologic folios were prepared, edit- 
ed and published, many questions of nomenclature arose which 
were not covered by the regulations, and the decision of these 
developed a system of precedents, analogous to the common 
law in distinction from statutory law. Experience in the appli- 
cation of the rules also discovered various ways in which the 
rules themselves might be improved, and after a period of thir- 
teen years it seemed best to give them a thorough revision, 
changing them wherever experience had found them at fault, 
and making them more specific by codifying some of the regu.- 
lations which had been developed through the decision of prac- 
tical questions. The work of revision was performed chiefly 
by a committee of eight geologists and paleontologists, but they 
solicited and received, at various stages of the work, the opin- 
ions, suggestions, and criticisms of all their colleagues, and 
their final draft was also modified by the Director before pub- 
lication. It is printed in the Twenty-fourth Annual Report, 
pages 23-27. 
Every published writing makes its contribution to usage in 
the matter of nomenclature, and thereby has a measure of in- 
fluence on the choice of words by others. As the literary prod- 
uct of the United States Geological Survey is large, the con- 
tribution made by its members to American usage in the mat- 
ter of geologic terms must be counted as important. While, 
therefore, the rules adopted by the Survey apply directly only 
to the publications of its members, they can not fail to have 
more or less influence on the practice of others. This gives the 
new rules a field of interest much wider than the corps to whose 
work they directly pertain, and is my justification for inviting 
attention, through the pages of this journal, to some of the 
changes they embody. 
In the earlier rules rocks were grouped, for purposes of the 
map, into four classes: (a) Fossilifcrous clastic, (b) super- 
ficial, (c) ancient crystalline, and (d) volcanic. In the new 
