THE DEVONIAN PERIOD. 435 



Devonian of the West. 



The Devonian system, so far as known, is absent from the larger 

 part of the Great Plains within the United States. This great expanse 

 of territory was probably land during the Devonian period. No Devo- 

 nian beds are found about the older formations in the Black Hills or 

 in the vicinity of Hartville, Wyo., where the succession of formations 

 has been studied in detail. The Helderberg is somewhat developed 

 farther southwest in the Arbuckle Mountains of Indian Territory * (Wood- 

 ford chert, see Appendix, Vol. III). The presence of Devonian beds 

 in Texas is also uncertain, though Helderbergian beds at least probably 

 occur in the southwestern part of that State. 2 The Devonian system has 

 little development in the Rocky Mountains, but is somewhat widespread 

 between the Rockies and the Sierras. It is represented in Arizona (Fig. 

 240), 3 Colorado, 4 Utah, 5 Nevada, 6 Wyoming (Fig. 247), and Montana, 7 

 and the Canadian Rockies. 8 Though its outcrops are not extensive, 

 its actual area is obviously much greater. In some places, as about 

 Globe, Arizona, the system is much faulted and affected by igneous 



bama, Stevenson, Gadsden; Georgia, Rome, Ringgold; Kentucky, Loudon, Rich- 

 mond; Kentucky-Virginia-Tennessee, Estillville; Pennsylvania, Brownsville, Connells- 

 ville, Elkland-Tioga; Pennsylvania-New York, Gaines; Tennessee, Briceville, Chat- 

 tanooga, Cleveland, Columbia, Kingston, Loudon, Maynardville, McMinnville, Morris- 

 town, Sewanee, and Standing Stone; Tennessee-North Carolina, Knoxville; Virginia- 

 Tennessee, Bristol; Virginia-West Virginia, Monterey, Pocahontas, Staunton, Taze- 

 well; West Virginia-Virginia, Franklin, Piedmont; West Virginia, Buckhannon. 



Details concerning the system are also found in the geological reports of the several 

 States where the system appears at the surface. 



»Tan\ Atoka (I. T.) folio, TJ. S. Geol. Surv. 



2 Hill, Physical Geography of the Texas Region, folio 3, topographic atlas, U. S. 

 Geol. Surv., p. 4. 



3 Blake, Jour Geol., Vol. IX, 1901, p. 68; and Am. Geol., Vol. XXVII, 1901 

 p. 164; Walcott, Am. Jour. Sci., Vol. XX, 1880, p. 221; and p. 436. 



4 Spencer, Am. Jour. Sci., Vol. IX, 1900, p. 125; Spurr, Mono. XXXI, U. S. Geol. 

 Surv., pp. 9-30; Girty, Professional Paper, No. 16, U. S. Geol. Surv., pp. 156-162. 



5 King, Geol. Expl. of the 40th Parallel, Vol. I; see also Weller, Jour. Geol., Vol. X, 

 pp. 423-32, 



6 Knight, Bull. 45, Wyo. Exp. Station; Yellowstone and Absaroka folios, U. S. 

 Geol. Surv.; Spurr, Bull. 208, U. S. Geol. Surv. 



'Little Belt, Fort Benton, Livingston, and Three Forks, Mont., folios, U. S. Geol. 

 Surv. 



8 Dawson, Bull. Geol. Soc. Am., Vol. XII, p. 68, and Ann. Rept. Geol. Surv. of 

 Canada, Vol. II, p. 19D. 



