322 



ARCHEOZOIC ERA 



Fig. 295. The white areas north of Mexico represent exposures of Archean; those 

 of Mexico represent lack of knowledge. The black areas represent exposures of Pro- 

 terozoic, and the lined areas represent Archean beneath later formations. The light 

 shading about the borders of the land represents the continental shelves, or, what is 

 the same thing, the area of the epicontinental seas for this continent. 



