212 



GEOLOGY. 



In the eastern part of the United States. 1 — In the eastern part of 

 the United States there are large areas of metamorphic rock which 

 vere formerly classed as Archean. As shown in Fig. 38, these rocks 



Fig. 87. 



-Figure showing peculiar polygonal structure in Proterozoic limestone in 

 northern Montana. (Willis, U. S. Geol. Surv.) 



occupy a large part of New England, the southeast corner of New 

 York, and parts of northern New Jersey, the South Mountain district 

 in Pennsylvania, and farther south, the wide belt of the Piedmont 

 plateau lying east of the Appalachian mountains from Pennsylvania 

 on the north to Alabama on the south. This belt of metamorphic 

 rocks contains formations that were sedimentary, and those that were 



1 See Bull. 86, U. S. Geol. Surv., and folios, U. S Geol. Surv. 



