Cambrian

Walcott, C.D., 1901, Cambrian Brachiopoda; Obolella, subgenus Glyptias; Bicia; Obolus, subgenus Westonia; with descriptions of new species: U.S. National Museum Proceedings, v. 23, p. 669-695.

Walcott, C.D., 1898, Cambrian Brachiopoda: Obolus and Lingulella, with description of new species: U.S. National Museum Proceedings, v. 21, p. 385-420.

Walcott, C.D., 1897, Cambrian Brachiopoda; genera Iphidae and Yorkia; with descriptions of new species of each, and of the genus Acrothele: U.S. National Museum Proceedings, v. 19, p. 707-718.

Walcott, C.D., 1891, Correlation papers; Cambrian: U.S. Geological Survey Bulletin 81, 447 p.

Walcott, C.D., 1891, The North American continent during Cambrian Time: U.S. Geological Survey Annual Report, 12th, Part 1, p. 523-568.

Walcott, C.D., 1890, The fauna of the Lower Cambrian or Olenellus zone: U.S. Geological Survey Annual Report, 10th, Part 1, p. 509-760.

Walcott, C.D., 1886, Second contribution to the studies on the Cambrian faunas of North America: U.S. Geological Survey Bulletin 30, 369 p.

Walcott, C.D., 1884, The Cambrian system in the United States and Canada [abs.]: Philosophical Society of Washington, Bulletin, v. 6, p. 98-102.

Ver Wiebe, W.A., 1932, Present distribution and thickness of Paleozoic systems: Geological Society of America Bulletin, v. 43, p. 495-540.

Tabachnik, R., 1979, Cambrian stratigraphy, in Nelson, C.A., ed., Grand Canyon: Los Angeles, University of California, Department of Earth and Space Sciences, Earth and Space Sciences Students Organization, ESSSO Guidebook 9, p. 23-27.