CONTRIBUTIONS TO ECONOMIC GEOLOGY, 1918.

PART II. MINERAL FUELS.

DAVID WHITE, G. H. ASHLEY, and M. R. CAMPBELL, Geologists in charge.

INTRODUCTION.

The Survey's "Contributions to economic geology" have been pubished annually since 1902. In 1906 the increase in the number of papers coming under this classification made it necessary to divide the contributions into two parts, one including papers on metals and nonmetals except fuels and the other including papers on mineral fuels. In 1915 the year included in the title was changed from the year in which the field work reported in these papers was done to the year of publication, and in consequence there was no volume entitled "Contributions to economic geology, 1914." The subjoined table gives a summary of these bulletins.

United States Geological Survey "Contributions to economic geology."

The date given is that of the complete volume; beginning with Bulletin 285 the papers have been Issued as advance chapters as soon as they were ready.

As the subtitle indicates, the papers included in these volumes are of two classes (1) short papers giving comparatively detailed descriptions of occurrences that have economic interest but are not

of sufficient importance to warrant a more extended description; (2) preliminary reports on economic investigations the results of which are published later in more detailed form. These papers are such only as have a direct economic bearing, all topics of purely scientific interest being excluded.

Brief abstracts of the publications of the year are given in the annual report of the Director. The complete list of Survey publications affords, by means of finding lists of subjects and of authors, further aid in ascertaining the extent of the Survey's work in economic geology.

The reports on work in Alaska have been printed in a separate series since 1904, the volumes so far issued being Bulletins 259, 284, 314, 345, 379, 442, 480, 520, 542, 592, 622, 642, and 662.

THE STRUCTURE OF PARTS OF THE CENTRAL GREAT

PLAINS.

By N. H. DARTON.

INTRODUCTION.

In the study of the geology of different parts of the central Great Plains many data have been accumulated that throw considerable light on the underground structure of the rocks. Most of the features observed have been described in previous publications, but others are set forth here for the first time. The area treated is shown on Plate I, on which the general structure is represented by contour lines. It is believed that a presentation of all available facts as to structural conditions in this region is warranted by the prevailing great interest in the possibility of the occurrence of petroleum and gas. Except near Florence and Boulder, Colo., and in Kansas from Eldorado to Eureka and eastward no traces of oil have been found in the central Great Plains region. As will be shown in this report, favorable structural features, such as domes

and anticlines,

is no evidence that the strata contain oil or gas in commercial pools these folds are more favorable for the location of tests than the basins or the monoclines. Only the drill can determine whether or

occur at many places in this region; and while there.

not oil is present.

The region is underlain by a thick succession of Cretaceous, Carboniferous, and older strata, including beds that in other regions vield oil or gas. Many holes have been sunk at intervals in the past, most of them to obtain water from the Dakota sandstone. Others have penetrated the upper part of the underlying "Red Beds," but except in places in central Kansas they have not tested the lower strata. Until the underground conditions are ascertained 1 Darton, N. H., Preliminary report on the geology and underground water resources of the central Great Plains: U. S. Geol. Survey Prof. Paper 32, 433 pp., 72 pls., 1905; Geology and underground waters of the Arkansas Valley in eastern Colorado: U. S. Geol. Survey Prof. Paper 52, 90 pp., 28 pls., 1906; Geology and underground waters of South Dakota: U. S. Geol. Survey Water-Supply Paper 227, 156 pp., 15 pls., 1909.

no boring can be regarded as a complete test in this region unless it penetrates all the older limestones and associated beds to the granite or schist basement. Moreover, most of the borings so far made have not been located in anticlines or domes favorable for oil or gas accumulation.

Shale and limestone (Marion formation)

FIGURE 1.-Sections showing underground relations of rocks along Atchison, Topeka & Santa Fe Railway between Strong and Ellinwood, Kans.

KANSAS.

CENTRAL KANSAS.

Very few facts are available as to the structure of the portion of Kansas lying between the ninety-sixth and one-hundredth meridians. The district is underlain by a thick succession of shales and limestones of Carboniferous age, above which to the west are sandstones and shales of Cretaceous age. The surface limit of the Cretaceous beds is shown approximately by a line on the map (Pl. I). In the area in which the older I rocks are exposed there is a general very low dip to the west, with local variations from place to place. The Cretaceous rocks dip in various directions, sloping into a wide, shallow syncline whose center is in the western part of Smith County and rising into a low dome whose axis passes near Dodge and Jetmore. Some of the general features in the central part of the area are shown in the sections (fig. 1).

The only district in which details of structure have been determined is about Cottonwood Falls and in adjacent