556 GEOLOGY. 



tinuous to the southward with the Carboniferous formations of the 

 United States. 



The system is widespread on both sides of the Gold range of British 

 Columbia. West of that range, the formations of the system (includ- 



Fig. 251. — Section showing the Carboniferous in the Sierras of central California. 

 C (Calaveras formation) = Carboniferous; J (Mariposa slates) = Jurassic; mdi 

 = metadiorite; ams = amphibolite schist; N = igneous rock of various sorts, of 

 Neocene age. Length of section about 6| miles. (Ransome, U. S. Geol. Surv.) 



ing the Lower Carboniferous) contain much volcanic rock, the greater 

 part of which was extruded before the close of the period. The igneous 

 activity of the time extended northward beyond the boundaries of 

 British Columbia into the little-known Northwest Territory, 1 and 

 southward into the United States. The Pennsylvanian system 2 is 

 continued northward into Alaska, where it is less wide-spread than the 

 Mississippian so far as present knowledge goes. In the arctic regions 

 of America, the Mississippian and Pennsylvanian are not differentiated, 

 but one or both are believed to be somewhat widespread. The same 

 systems also find meager representation in Mexico and Central America. 



Sections of the Mississippian and Pennsylvanian Systems. 



The following sections of the Pennsylvanian system (together 

 with the Mississippian and in some cases the Permian) at various 

 points within the United States, supplement those given in the 

 Appendix and give some idea of the range, variations, and relations 

 of the system: 



1 Dawson, Science, March 15, 1901. 



2 Brooks, Professional paper, p. 19. 



