THE STORY OF NINETEENTH-CENTURY SCIENCE 



Kegarding our own continent, for example, we learn 

 through the researches of a multitude of workers that 

 in the early day it was a mere archipelago. Its chief 

 island the backbone of the future continent was a 

 great Y-shaped area surrounding what is now Hudson 

 Bay, an area built up, perhaps, through denudation of a 

 yet more ancient polar continent, whose existence is only 

 conjectured. To the southeast an island that is now t-he 

 Adirondack Mountains, and another that is now the 

 Jersey Highlands, rose above the waste of waters ; and 

 far to the south stretched probably a line of islands now 

 represented by the Blue Eidge Mountains. Far off to 

 the westward another line of islands foreshadowed our 

 present Pacific border. A few minor islands in the in- 

 terior completed the archipelago. 



From this bare, skeleton the continent grew, partly by 

 the deposit of sediment from the denudation of the orig- 

 inal islands (which once towered miles, perhaps, where 

 now they rise thousands of feet), but largely also by the 

 deposit of organic remains, especially in the interior sea, 

 which teemed with life. In the Silurian ages, inverte- 

 brates brachiopods and crinoids,and cephalopods were 

 the dominant types. But very early no one knows just 

 when there came fishes of many strange forms, some 

 of the early ones enclosed in turtlelike shells. Later 

 yet, large spaces within the interior sea having risen to 

 the surface, great marshes or forests of strange types of 

 vegetation grew and deposited their remains to form 

 coal beds. Many times over such forests were formed, 

 only to be destroyed by the oscillations of the land sur- 

 face. All told, the strata of this Paleozoic period aggre- 

 gate several miles in thickness, and the time consumed 

 in their formation stands to all later time up to the 



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