The field study of the geology of the De Queen and Caddo Gap quadrangles extended over a period of many years, and although the scientific and economic results from the study are here set forth fully for the first time in a single report, a number of publications have been issued that have presented some of the more important results.

The field work was begun in 1907 and continued intermittently until 1925. The work in 1907 was done under a cooperative agreement between the United States Geological Survey and the Arkansas Geological Survey and involved primarily an investigation of the slate deposits of west-central Arkansas but also the mapping of the rocks in the mountainous part of the Caddo Gap quadrangle. In that year A. H. Purdue, State geologist of Arkansas, had charge of the work and was assisted by R. D. Mesler and H. D. Miser. All the subsequent work in the Caddo Gap quadrangle, as well as all in the De Queen quadrangle, was done by the United States Geological Survey. The work since 1907 is briefly outlined below. In 1908 Mr. Purdue, assisted by Mr. Miser, completed the mapping of the rocks of the Caddo Gap quadrangle with the aid of valuable suggestions from C. W. Hayes, chief geologist, J. A. Taff, and E. O. Ulrich, who visited the field for several days. In 1910 Mr. Purdue, assisted by Mr. Miser, reviewed a part of the previous work in the Caddo Gap quadrangle and mapped the rocks in most of the mountainous portion of the De Queen quadrangle. In 1911 these geologists did additional work in both the De Queen and Caddo Gap quadrangles, and in 1912 Mr. Miser, assisted by Mr. Mesler, completed the mapping of the rocks in the De Queen quadrangle and then reviewed some of the earlier work in the Caddo Gap quadrangle. In 1913 Arthur Keith, and Messrs. Purdue and Miser spent several days in a field conference in the Caddo Gap quadrangle. During the conference the first identifiable fossils in the Blaylock sandstone, of Silurian age, were discovered. In 1914 Mr. Miser obtained a small collection of fossil plants from the Stanley shale near Gillham, Ark., also the first fossils from the Arkansas novaculite. In 1916 he made a special study of some of the mineral deposits of the quadrangles, including the deposits of diamonds, manganese ore, gravel, and asphalt, and in 1917 he revisited the diamond mines. An investigation of the volcanic ash and tuff in the "Bingen formation," of Upper Cretaceous age, in the Caddo Gap quadrangle and adjoining areas to the south and southwest was made in 1923 by Clarence S. Ross and Mr. Miser.

Also in that year other fossil plants were collected from the Stanley shale at the earlier discovered locality near Gillham by Mr. Miser. (See pl. 9, A.) The aggregate time spent in collecting fossils at this locality was eight days, so scare are the fossils and so difficult are the conditions for collecting them. Besides the above work the authors made frequent reconnaissance studies of adjoining areas, and Mr. Miser was joined in 1923 by C. W. Honess for a field conference of a few days in the De Queen and Caddo Gap quadrangles. In 1925 Mr. Miser joined in the field Messrs. L. W. Stephenson and C. H. Dane for a few days in a study of the " Bingen " (Woodbine and Tokio) and other formations of Upper Cretaceous age in and near the Caddo Gap quadrangle. Mr. Dane was making at that time a special study of the deposits of Upper Cretaceous age in southwestern Arkansas under a cooperative agreement between the United States Geological Survey and the Arkansas Geological Survey. For some of the information on the Tokio formation the present writers are indebted to Mr. Dane.