Tecumseh, Weston, Cherryvale, and Cherokee shales appear to have a much broader extent, and any thick bands of red shale that may be encountered in drilling will probably be parts of one or another of these formations.

Beds of black shale are of much less value as horizon markers. The color is not so distinctive as red, and a wet blue shale may sometimes be recorded as black. Furthermore, in northeastern Oklahoma black shales are not confined to a few horizons but have been found in every shale formation between the Oread limestone and the base of the Pennsylvanian series. It may be stated as a general rule, however, that thick layers of black shale are more numerous near the base of the Pennsylvanian than in its upper portion, and that thick, closely spaced layers of this color will not be encountered above the Pawnee limestone.

A third point that may lead to confusion and serious errors in interpreting the data furnished by well records is the inability or neglect of some drillers to distinguish between limestone and sandstone. Limestones are recorded as sandstones and vice versa because the driller's decision as to the character of the rock is based on the way it cuts or dulls the bit, the rapidity with which it is penetrated, and the "feel" of the impact of the drill as transmitted by the drilling cable, more than on examination of the cuttings.

If these failings could be overcome the record of churn-drill operations would be sufficiently accurate to justify very definite statements concerning the nature and age of the strata in the 2,100 feet immediately underlying the surface of the area.

MISSISSIPPIAN SERIES.

Below the rocks belonging to the Pennsylvanian series are older sediments. Although no drilling in the area under consideration has gone deep enough to ascertain the nature of the rocks that lie more than 200 or 300 feet below the horizon of the Cherokee shale, some notion of their general character may be obtained by consideration of the features which they show at their outcrops in northeastern Oklahoma, southwestern Missouri, and northwestern Arkansas and by study of the records of deep wells that have been drilled in Caney and Iola, Kans.

The Mississippian series in southwestern Missouri, northwestern Arkansas, and northeastern Oklahoma is made up of rock of Chester age above and the Boone limestone below. The rocks of Chester age are black and dark-colored shales and equally somber-colored limestones. No such series of dark-colored rocks has been recorded in the logs of deep wells drilled in or near the northwest corner of the Pawhuska quadrangle, so it may be assumed that the Chester epoch

is not represented by sediments in the area under consideration, although the Boone limestone, which lies unconformably below the rocks of Chester age in eastern Oklahoma, is believed to underlie the entire area.

The Boone limestone in northeastern Oklahoma attains a maximum thickness of about 350 feet, the greater part of which is interstratified chert and limestone. Both limestone and chert are light colored.1

The deep well drilled at Caney, Kans. (see Pl. XV), penetrated 262 feet of limestone which immediately underlies the Cherokee shale and which is ascribed to the Boone formation by Schrader.2 The Iola deep well (Pl. XV) penetrated 168 feet of so-called "Mississippi lime" and 24 feet of arenaceous limestone, both of which probably belong to the Boone formation and give it a thickness of 192 feet. As Iola is about 70 miles northeast of Caney, it may be concluded that the Boone thickens toward the southwest and is very probably thicker in northeastern Oklahoma than it is in central and southern Kansas. This conclusion is strengthened by the thickness observed at its outcrop in northeastern Oklahoma. A fair estimate for its thickness in the northwest corner of the Pawhuska quadrangle is 350 feet.

DEVONIAN ROCKS.

It is estimated by the writer that at least 150 feet of black shale, sandstone, and perhaps limestone of Devonian age lie unconformably below the rocks of the Carboniferous system. This estimate is based on the measured thickness of about 100 feet at the outcrop of these beds in northeastern Oklahoma,* the observed tendency of the Devonian rocks to thicken toward the west in the region where they crop out, and on the thickness of these rocks in a well drilled at Caney, Kans. (Pl. XV), which penetrated 35 feet of black bituminous shale, 207 feet of limestone, and 11 feet of sandstone ascribed by Schrader to the Devonian.

The Chattanooga shale, which is the youngest Devonian rock in this region and therefore the one which will be first encountered in a well, is a black carbonaceous shale of uniform character. In most places it contains so high a percentage of organic matter that when

1 Snider, L. C., Geology of a portion of northeastern Oklahoma Oklahoma Geol. Survey Bull. 24, p. 26, 1916. Siebenthal, C. E., Mineral resources of northeastern Oklahoma: U. S. Geol. Survey Bull. 340, p. 190, 1907.

Schrader, F. C., U. S. Geol. Survey Geol. Atlas, Independence folio (No. 159), p. 4,

1908.

3 Haworth, Erasmus, Kansas Univ. Geol. Survey, vol. 9, pl. 6, 1908.

Snider, L. C., Geology of a portion of northeastern Oklahoma: Oklahoma Geol. Survey Bull. 24, p. 20, 1916.

5 Schrader, F. C., U. S. Geol. Survey Geol. Atlas, Independence folio (No. 159), p. 4,

freshly broken it emits an odor of decay. This shale is easily recognized at its outcrop and should be identified with almost equal facility when it is encountered in borings.

The Sylamore sandstone, the basal member of the Chattanooga shale in some localities in northeastern Oklahoma, southwestern Missouri, and northwestern Arkansas, is phosphatic, coarse-grained, locally conglomeratic sandstone which has a maximum observed thickness in Oklahoma of 35 feet. It is bounded by unconformities, so that no uniform thickness may be assumed for it. It is absent in much of the area where it would be exposed at the surface if it were present, and the same conditions presumably continue toward the west.

SILURIAN (?), ORDOVICIAN, AND CAMBRIAN ROCKS.

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are

Silurian rocks are not known to be present in northern Oklahoma. Siebenthal says that "formations of Silurian age wanting in all the western part of the Ozark region." However, it is entirely possible that they are present below the surface of the area under consideration. Schrader assigns to this system 375 feet of crystalline gray, bluish-gray, and brown limestone, which was passed through in drilling the deep well at Caney, Kans. (Pl. XV), and correlates it with the St. Clair marble, which is present in eastcentral Oklahoma.2

Below the Silurian, if present, are rocks of Ordovician age. The deep wells at Caney, Neodesha, and Iola, Kans. (Pl. XV), penetrate magnesian limestones, dolomites, shales, and sandstones of this age, which also crop out in the Ozark region and in eastern Oklahoma. Notable among the sandstones is the St. Peter, which is more than 100 feet thick in some parts of eastern Oklahoma and southwestern Missouri. It is very uniform in character and of broad distribution. Schrader believes that a sand 46 feet thick that was encountered in the Caney deep well about 897 feet below the base of the Chattanooga formation corresponds to the St. Peter sandstone.

Below the St. Peter sandstone there are limestones, dolomites, and sandstones probably extending considerably below the limit of 4,000 feet which was mentioned as the thickness of strata that would be discussed. The lowest sedimentary formation that would be encountered in a well 4,000 feet deep drilled near the eastern edge of the

1 Taff, J. A., U. S. Geol. Survey Geol. Atlas, Tahlequah folio (No. 122), p. 2, 1905. Adams, G. I., and Ulrich, E. O., U. S. Geol. Survey Geol. Atlas, Fayetteville folio (No. 119), p. 3, 1905.

2 Taff, J. A., op. cit., p. 3.

3 Siebenthal, C. E., Origin of the zinc and lead deposits of the Joplin region: U. S. Geol. Survey Bull. 606, p. 25, 1915.

4 Schrader, C. F., U. S. Geol. Survey Geol. Atlas, Independence folio (No. 159), p. 4, 1908.

RECORDS OF DEEP WELLS AT CANEY, NEODESHA, AND IOLA, KANS., SHOWING THE CHARACTER OF THE UPPER PART OF THE PRE-PENNSYLVANIAN ROCKS OF SOUTHEASTERN KANSAS.