. Annual report of the United States Geological Survey to the Secretary of the Interior . O. carinata. G. washitaensis. texanus. Ammonites sp. Hamites fremontii. A. brazoensis. Ino-ceramus munsoni, I. comancbeanus. Fig. 32.—Geologic section, Denison, Texas. 268 BLACK AND GRAND PRAIRIES, TEXAS. : rrr. ~| Turritella 1—V < <- O. quadrzplicata. Gervilliopsis. .subgroup, consisting of the Main Street limestone and Grayson marl,the term Pottsboro may be used. The lower part of the Denton subgroup consists of beds of bluemarly clays, terminating above
. Annual report of the United States Geological Survey to the Secretary of the Interior . O. carinata. G. washitaensis. texanus. Ammonites sp. Hamites fremontii. A. brazoensis. Ino-ceramus munsoni, I. comancbeanus. Fig. 32.—Geologic section, Denison, Texas. 268 BLACK AND GRAND PRAIRIES, TEXAS. : rrr. ~| Turritella 1—V < <- O. quadrzplicata. Gervilliopsis. .subgroup, consisting of the Main Street limestone and Grayson marl,the term Pottsboro may be used. The lower part of the Denton subgroup consists of beds of bluemarly clays, terminating above by conspicuous indurations of oysterbreccia made up largely of Gryphcea washitaensis accompanied by Ostrea carinata. The Weno subgroup ischaracterized by black and brown ferru-ginous clays and sands. At the base thissubgroup consists of laminated beds weath-ering brown, with occasional layers of im-mense rounded, fissile, lens-shaped indurations, generally brown in color. At thetop of this subgroup is a conspicuous lime-stone bed known as the Quarry limestone,which in turn is succeeded by the Pawpawbeds, composed of dark clays and sandy fer-ruginous strata, oxidizing into ironstonewhich in places is almost indistinguishablefrom the Dakota sandstone. The uppermost or Pottsboro subgroupis characterized by beds of impure yellowlimestone, which under
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