THE PENNSYLVANIAN PERIOD 



629 



Figs. 442 to 444 show the positions and relations of the Missis- 

 sippian and Pennsylvanian systems at various points in the west. 

 In most cases the sections are from regions where the strata have 

 been much disturbed by folding, faulting, and the irruption of 

 igneous rock. 



North of the United States, Carboniferous strata (largely 

 Mississippian) outcrop on the west side of the northward continu- 



Fig. 443. Section showing the position and relations of the Carboniferous 

 system at a point in Colorado. ^B = Archean; -G = Cambrian (Sa- 

 watch quartzite); O = Ordovician (Yule limestone); M = Mississip- 

 pian (Leadville limestone); Cw (Weber formation) and Cm (Maroon 

 conglomerate) = Carboniferous; / (Gunnison formation) = Jurassic; 

 Kd (Dakota formation), Kb (Benton shale), Kn (Niobrara limestone), 

 and Km (Montana formation) = Cretaceous. Length of section about 

 6 miles. (Eldridge, U. S. Geol. Surv.) 



Fig, 444. Section showing the Carboniferous in the Sierras of central Cali- 

 fornia. C (Calveras formation) = Carboniferous; J (Mariposa slates) 

 = Jurassic; mdi = metadiorite; ams = amphibolite schist; A T = ig- 

 neous rock of various sorts, of Neocene age. Length of section about 

 6^ miles. (Ransome, U. S. Geol. Surv.) 



ation of the Great Plains, and the strata here are probably contin- 

 uous beneath younger beds which occupy the surface between them, 

 and they are probably also continuous to the southward with the 

 contemporaneous formations of the United States. Strata of the 

 same age are found on both sides of the Gold Range of British 

 Columbia. West of this range, much volcanic rock, the greater 

 part of which was extruded before the close of the period (p. 601), 

 appears in the system. The system is continued northward into 

 Alaska, 1 where it is less wide-spread than the Mississippian, so far 

 1 Brooks, Professional Paper 45. 



