THE CAMBRIAN PERIOD. 



269 



Figs. 113 and 114, at two points in the Appalachian mountains; and 

 Fig. 115, near Holyoke, Mass. These several sections give a fairly 

 adequate idea of the present position and relations of the system. In 

 Figs. 102, 107, and 112 the structure of the Cambrian is relatively 

 simple and the rocks are not metamorphosed. In Fig. 103 the beds 

 are gently folded and erosion has discovered the Cambrian beds at the 







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Fig. 116.— Figure showing an isolated remnant (a dying hill) of Potsdam sandstone 

 in central Wisconsin. The remnant has been isolated by erosicri. 



tops of the anticlines. The rocks are not metamorphic. In Fig. 113 

 the beds are more crumpled at the right, and faulted as well as folded 

 at the left, and the rocks are somewhat metamorphic. In Fig. 114 

 close folding and faulting are represented, and the metamorphism of 

 the rocks has proceeded farther, though not to extremes. In Fig. 115 

 the crumpling due to profound dynamic action is more pronounced, 

 and here the rocks are highly metamorphic. 



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. 



