GEOLOGY AND PALEONTOLOGY. 27 
After the scheme for the publication of the map had assumed final 
form the necessity for these broader studies was less urgent and the 
work of the Survej^ returned more and more to economic lines. The 
early economic work was confined to the investigation of the ores of 
the precious metals, but it is now distributed over the whole field of 
mineral production, embracing- the nonmetalliferous minerals as well 
as the metalliferous ores. Of the 53 parties engaged in field work 
daring the year 1903-4, 24 were engaged in work which was primarily 
economic, while 14 others were employed on work which was more or 
less directly economic in character. 
The division of geology and paleontology is now under the general 
direction of the geologist in charge. Since, however, the work is 
somewhat varied, scientific control along various lines is vested in 
chiefs of the following sections: 
Areal geology. 
Pleistocene geology. 
Pre-Cambrian and metamorphic geology. 
Petrology. 
Paleontology. 
Economic geology of metalliferous ores. 
Economic geology of nonmetalliferous minerals. 
The first-named section has immediate charge of the work of making 
a geologic map of the United States. The sections of Pleistocene and 
pre-Cambrian geology represent specializations of that map work. 
The petrologic section is concerned with the study of the rocks them- 
selves, the paleontologic with the fossils in the rocks, and the two 
remaining sections are concerned with the metalliferous ores and the 
nonmetalliferous minerals. 
The section chiefs are in effect consulting geologists who help the 
individual workers in the formulation and solution of their problems. 
Each field party works under the supervision of one or more section 
chiefs, selected according to the nature of the problems of the area. 
Before publication all manuscripts are submitted for criticism and 
approval to the, chiefs concerned. 
The main purpose of the Survey is defined by law to be the making 
of a geologic map of the United States. In discriminating the different 
formations and determining the complicated structure of the various 
mining districts, however, many facts of interest and importance in 
themselves are brought out. With very little additional work it is 
usually possible to give a fairly complete account of the ore bodies, 
and such work absorbs a ver}^ large share of the time and energy of 
the corps. This is as it should be, since one of the main purposes of 
the map is to aid in the development of our natural resources. 
Geologic maps are valuable in many ways. They show the areas 
within which coal, iron, and other useful minerals occur, the limits of 
the artesian basins, the course of metalliferous veins, and many other 
