370 HISTORICAL GEOLO&Y. 



not known. The map (Fig. 168) represents the present 

 state of our knowledge on this subject. It is probable, 

 however, that the Eastern land-mass (Blue Ridge Archaean 

 area) was larger than represented, having been subse- 

 quently covered by later deposits, and partly, even now, 

 by the Atlantic Ocean. 



The change in the rocks, in passing westward from the 

 Appalachian region, is completely explained by the posi- 

 tion of the Appalachian region and the subsequent f orma- 



FIG. 168. Map of physical geography of Primordial times : existing seas and lakes, 

 black ; continental seas of that time, light shade ; land of that time, white. The 

 white dotted line shows the probable shore-line of 2 at this time. 



tion of the mountains. This region was then the marginal 

 bottom of the interior sea, receiving abundant and coarse 

 sediments, which became finer and thinner seaward. 

 This thick marginal line then yielded, was strongly folded 

 and highly metamorphosed in the act of mountain- 

 making which took place at the end of the Paleozoic. 



