LETTER OF TRANSMITTAL. DEPARTMENT OF THE INTERIOR, Washington, D. C., March 21, 1896. SIR: I take pleasure in transmitting herewith a manuscript entitled "A brief contribution to the geology and paleontology of northwestern Louisiana," by T. Wayland Vaughan. This paper embraces the valuable results of Mr. Vaughan's observations in an important region of the United States, and I recommend that it be published as a bulletin of the Survey. A BRIEF CONTRIBUTION TO THE GEOLOGY AND PALEONTOLOGY OF NORTHWESTERN LOUISIANA. By T. WAYLAND VAUGHAN. PREFATORY NOTE. The following short paper gives the results of some studies that I have made on the geology and paleontology of northwestern Louisiana. This contribution is necessarily of a fragmentary nature, partly on account of the conditions under which the studies have been prosecuted and partly from an entire lack of topographic maps of the area discussed. In the American Geologist for April, 1895, I published a paper entitled "The stratigraphy of northwestern Louisiana." The greater part of that paper, with some verbal changes, is republished here as a stratigraphic introduction. In the lists of the species, references to the publications where they were first described are omitted, because in Prof. G. D. Harris's report on the Tertiary geology of southern Arkansas numerous references are given. Professor Harris has written a "Monograph of the Tertiary Mollusca of Texas" (not yet published), and Mr. C. W. Johnson, curator of the museum of the Wagner Free Institute of Science, of Philadelphia, is engaged in making a catalogue, with bibliographic references, of the species in the Isaac Lea memorial collection of Eocene fossils. These publications will contain references to practically all of the species listed in the present paper. Dr. William H. Dall has prepared a paper, which will probably appear in the Eighteenth Annual Report of the Survey, dealing with the nomenclature and correlation of the Tertiary beds of the United States. In this contribution Dr. Dall has shown that the Vicksburg and the Grand Gulf and the beds hitherto denominated Lower Miocene should be considered Oligocene, the first belonging to the Lower Oligocene and the second to the Upper Oligocene. Through the courtesy of Dr. Dall, I have utilized that classification in the present paper. I am under obligations to Dr. William H. Dall, Prof. Angelo Heilprin, Mr. H. A. Pilsbry, Dr. C. E. Beecher, and Prof. R. P. Whitfield for access to the collections under their charge. Dr. Dall has permitted 'Annual Report of the Geological Survey of Arkansas for 1892, Vol. II, 1894. me to catalogue the material from Louisiana in the United States National Museum. In the summer of 1892 I was assistant to Dr. Otto Lerch during his survey of the hills of northern Louisiana, and he submitted to me for study the collection of the Louisiana survey. Prof. G. D. Harris has given me much assistance in identifying many of the fossils. Mr. Robert T. Hill, during the field season of 1894, gave me the opportunity to return to Louisiana to study further the Eocene of that State. Through his kindness I have been allowed time to continue my study of the fossils during the season of office work. STRATIGRAPHY OF THE REGION. AREA DEFINED. The area here described is that portion of Louisiana bounded in a general way by the Arkansas and Texas State lines, by the Ouachita River as far south as Harrisonburg, by a line running thence to Alexandria on the Red River, and thence northeast to a point west of Mansfield on the Sabine River. This area has been the subject of study by several geologists. Conrad, as early as 1834,' announced the existence of the Eocene in it from fossils sent him. Later Hilgard, Hopkins, Johnson, Lerch, Harris, and McGee have done field work there. The publications of these geologists will be alluded to as reference to their work becomes necessary. THE CRETACEOUS. The existence of Cretaceous strata in Louisiana was first indisputably established by Hilgard in 1869.2 Subsequently Hopkins, Johnson, and Lerch have noted the occurrence of Cretaceous in the State. Dr. Lerch gives a list of the localities of these rocks in his preliminary report3 upon the geology of the hills of Louisiana. Cretaceous outcrops have been found in northern Louisiana, in the parishes of Webster, Bienville, Natchitoches, Winn, and Rapides. Hilgard observed that these outcrops when mapped form a line trending from northwest to southeast. Associated with them are salt deposits; hard limestone, sulphur, and gypsum are not infrequent. On secs. 31 and 32, T. 10 N., R. 4 W., near Atlanta, in Winn Parish, there outcrops a hard blue limestone, which is traversed by minute fissures. In these fissures a small amount of gold occurs. In these rocks Exogyra costata has been found. As this fossil is characteristic of the Glauconitic division of the Upper Cretaceous, the strata in Louisiana bearing it must be considered as of Glauconitic age. 1Jour. Acad. Nat. Sci. Phila., Vol. VII, 1834, p. 120. "Preliminary report of a geological reconnoissance of Louisiana: De Bow's New Orleans Review, September, 1869, p. 11. 3 A preliminary report upon the hills of Louisiana: Bulletin of the Louisiana Experiment Station, 1893, Part II, p. 72. Hilgard1 mentions Gryphæa pitcheri also; but he is without doubt mistaken in his identification, as G. pitcheri is a Comanche series fossil, and does not occur in the Upper Cretaceous. The relations of the Eocene to the Cretaceous, as conceived by Hopkins, are shown in a section across the State, published in his first report. He indicates that there are knobs of Cretaceous, around which the Eocene was deposited, but does not state explicitly the relations existing between the two series. Dr. Lerch gives the following explanation: If we connect the above localities we obtain an irregular line with a northwesterly trend, revealing the distribution of the Cretaceous deposits in north Louisiana as far as explored over 1,000 feet in thickness. Nowhere outside of the outcrops have bores reached the Cretaceous, not even in the nearest vicinity; wells of considerable depth have penetrated the shales of the Lower Lignitic and Marine Claiborne which surround these islands. It is most probable, however, that at Shreveport the artesian bore, 1,100 feet in depth, has penetrated the Tertiary strata, and that the water flows from the Upper Cretaceous sands. Judging from the bores and exposures of this substructure of Louisiana, and excluding the overlying later deposits, it represents a ridge with steep hillsides and occasional high peaks with almost perpendicular declivities. The Exogyra costata and the Gryphæa pitcheri, found in close proximity in these outcrops, as well as the Eocene directly overlying and resting against the Cretaceous, seem to prove that at the close of Mesozoic time enormous plutonic forces convulsed, fractured, faulted, and folded the Cretaceous strata, throwing up mountain chains of vast extent and raising them far above the waters of the Gulf. It seems to us more than possible that these grand disturbances involve the whole of the Southern Cretaceous, and that the enormous downthrow along the Balcones and the basaltic outbreaks along that fault are contemporaneous with the origin of the mountain chain in the Tertiary of that State and of Louisiana. In the basins and embayments formed the Eocene strata were deposited, the very existence of which proves that there was no interval of a land period between the Cretaceous and Tertiary in this State, and if we could remove the covering mantle we would see the chains and peaks of limestone ranges formed at the close of the Middle Ages of our planet altered somewhat by later erosion and denudation. I am not prepared to agree with Dr. Lerch as to the correlation of the disturbance in Louisiana succeeding the close of the Cretaceous deposition, with the times of the Balcones faulting and the Pilot Knob volcanic activity. I will emphasize the following facts, however. The Cretaceous outcrops in the area under discussion have a general southeast and northwest trend, with knobs or peaks projecting along the line, and around these knobs the Eocene has been deposited. The occurrence of many of these projecting peaks would indicate a period of erosion intervening between the close of the Cretaceous and the beginning of the Eocene. Furthermore, the Cretaceous at the Winn Parish marble quarry is almost horizontal, the limestone rising as a 'Preliminary report of a geological reconnoissance of Louisiana, p. 11. "First Annual Report of the Geological Survey of Louisiana, p. 78, in the Louisiana State Univer. sity Report for 1869, published 1870. *A preliminary report upon the hills of Louisiana: Bulletin of the Louisiana Experiment Station, 1893, Part II, p. 72. *The Pilot Knob volcano was probably active during late Cretaceous time, whereas the Balcones, faulting took place much later. |