446 H. D. Campbell — Cambro-Ordovician Limestones. 



C. D. Walcott* found Lower Cambrian fossils. The forma- 

 tion is superjacent to the quartzites and shales of the Balcony 

 Falls section. 



Bitena Vista shale. — Bright variegated shale is conspicuous 

 in the bluffs of James River between Sherwood and Buchanan, 

 and along the road between Sherwood and Natural Bridge. 

 Red bands predominate, but green, yellow, and brown colors 

 are common. Mottled blue limestone beds alternate with the 

 shale in the lower part, and it passes by a succession of shale 

 and limestone beds into the superjacent limestone. In this 

 formation C. D. "Walcottf found a Ptychoparia closely related 

 to species from the Middle Cambrian beds of Tennessee. The 

 formation is from 600 to 900 feet thick. It receives its name 

 from Buena Yista, Ya., where it is well developed. 



Natural Bridge limestone. — The formation consists princi- 

 pally of heavy -bedded gray and light blue magnesian limestones 

 with thin siliceous laminse as a conspicuous feature, especially 

 upon weathered surfaces. Beds of white and pinkish dolomite 

 occur now and then. Calcareous sandstone strata from a few 

 inches to eight feet thick are occasionally prominent. Black 

 chert occurs in nodules more or less throughout the formation, 

 but heavy beds of chert are usually very conspicuous near the 

 top. Specimens of Lingulepis and Obolus were discovered by 

 C. D. Walcott in this formation two miles below Buffalo 

 Mills on Buffalo Creek in June 1898, thus establishing by fos- 

 sils the age of part of this limestone as Cambrian. Fossils 

 from 300 or 400 feet below the top of this formation make 

 the age of its upper beds Beekmantown (Calciferous)4 



On account of the difficulty of determining the geologic 

 structure in this section, the total thickness of the formation 

 has not been accurately determined, but measurements which 

 were made in a continuous series where there was no indica- 

 tion of folding or faulting indicate a thickness of over 3500 

 feet. The Natural Bridge and its canyon display part of this 

 limestone, and hence the name. 



Murat limestone. — Superjacent to the heavy chert beds of 

 the Natural Bridge limestone occurs a massive gray crystalline 

 limestone containing bryozoa and other fossils in abundance. 

 About 125 feet of it are well exposed along Buffalo Creek at 

 Murat, Ya., whence the formation takes its name. Its lower 

 portion often contains chert nodules. The deep red clay soil 

 resulting from the Murat limestone is conspicuous in contrast 

 with the gray cherty soil from the top of the Natural Bridge 

 formation. 



* This Journal, July 1892, p. 53. 



f Ibid., p. 52. 



JK. S. Bassler, Bull. U. S. Geol. Surv. No. 243, 1905, p. 315. 



