Contributions to the geology and paleontology of San Juan County, New Mexico; 1. Stratigraphy of a part of the Chaco River valley

This preliminary paper is an attempt to set forth the principal features of the stratigraphy in a part of the San Juan Basin-to describe the succession of strata irrespective of possible correlations and thereby to establish a type section for the formations exposed and to bring out their relations to the strata immediately above and below. The paper presents only a part of the data collected by a field party of the United States Geological Survey in the season of 1915, in charge of the writer, and does not describe the economic resources of the area, such as coal, nor the general geologic problems. In mapping formation boundaries, streams, roads, and other surface features, the plane table and alidade were used. Where the slopes are steep and the strata nearly norizontal, sections were measured directly with a hand level. Elsewhere the alidade was employed for obtaining distances and differences in elevation, and the thickness of the intervening strata was calculated from these data. ~ossils were collected at localities whose positions were accurately determined, both stratigraphically and geographically. The accompanying papers on the paleontology of the area, by C. W. Gilmore, T. W. Stanton3 and F. H. Knowlton/ discuss the fossil collections made by the field party. For these collections and a considerable part of t~e. other data, including mapping, much credit IS due to John B. Reeside, jr., who assisted the writer both in the field and in the office, and to H. R. Bennett, who assisted in