490 



GEOLOGY 



Over great areas in the interior (Missouri, Wisconsin, Texas, etc.) 

 the strata still remain in horizontal or nearly horizontal position, 

 while in other regions they have been tilted, folded, and faulted. 

 Where close folding has taken place, the rocks have been more or 

 less metamorphosed. In extreme cases the sandstones have been 

 converted into quartz schists, the shales into slates and schists, 

 and the limestones into marble. Fig. 361 shows the general position 

 of the Cambrian strata (-6 1 ) over much of the interior, and Figs. 367 



X, /<?' 



'iV* x * !*>->*. ^<V>/ X ' N - 



ie relations of Cambrian and other formatio 



Fig. 368. Section showing the relations of Cambrian and other formations 

 at a point in Colorado a little north of Leadville. jtgn, Archean; 

 Gs, Cambrian (Sawatch quartzite); Cmr, Carboniferous (Maroon forma- 

 tion); /MJ, Jurassic (Wyoming formation); Ip and qp, igneous rocks. 

 (Emmons, U. S. Geol. Surv.) 



and 368 illustrate their position and relations where they have 

 been folded and faulted. 



Close of the Cambrian. No physical changes of great importance 

 seem to have marked the close of the Cambrian period in America. 

 Nowhere in our continent, so far as now known, were mountains 

 made at this time, and nowhere were great areas of sea-bottom 

 converted into land, though local unconformities 1 between this 

 system and the next record local changes in the sites of 

 deposition. 



In Other Continents 



Europe. 2 In Europe, as in North America, wide-spread defor- 

 mation before the beginning of the Cambrian converted large areas 



1 Gushing. Bull. Geol. Soc. Am., Vol. XIX, p. 155. 



2 The best summary, in English, of the Cambrian of Europe, is found in 

 Geikie's Text-book of Geology, 4th ed., Vol. II. 



