292 PALAEOZOIC SYSTEM OF ROCKS. 



above (Fig. 265). It may be stated roughly to embrace all that part 

 included between the Great Lakes on the north, the Blue Kidge of the 

 Appalachian chain on the east, the Prairies on the west, and Middle 

 Alabama and Southern Arkansas on the south. It includes the richest 

 portion of our country. Besides this great continuous area there are 

 also areas of imperfectly known size and shape in the Rocky Mount- 

 ain region, and on either side of the Sierra Nevada. 



Physical Geography of the American Continent. — At the beginning 

 of the Palaeozoic era (Primordial) the land was substantially the Ar- 

 chcean area, already described, plus certain areas of Archaean rocks which 

 were then land, but have been subsequently covered by later deposits — 

 minus certain Archaean areas which have been subsequently exposed 

 by erosion. The map (Fig. 266) * is an attempt to represent approxi- 

 mately the continent of that time. It consisted (1) of a great Northern 

 land-mass corresponding roughly to the Canadian V-shaped Archaean 



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Fig. 266.— Map of Primordial Times: Black, existing seas and lakes; light shade portions of the 

 continent then covered bv sea: white areas, then land; when limits doubtful, surrounded by 

 dotted line. In case of area 2 the land extended beyond the present shore-line to an unknown 

 distance, represented by the white dotted line. 



area. (2.) An Eastern land-mass, including the Appalachian Archaean 

 area, but extending far beyond it to the eastward (for the coast strata 

 here are Cretaceous and Tertiary, resting directly on Archaean, without 

 any Palaeozoic between), and probably beyond the present limits of the 



* A map similar to the above, but containing also small scattered patches of Archaean 

 exposures, is sometimes spoken of as an Archaean map of North America, or map of 

 Archaean land. It must be borne in mind, however, that it represents indeed land of 

 Archaean strata, but, for that very reason, not of Archaean time, but of Silurian time. 



