AREAS OF CONTINENTAL PB0GRE88 IN NORTH AMERICA, 

 AND THE INFLUENCE OF THE CONDITIONS OF THESE 

 AREAS ON THE WORK CARRIED FORWARD WITHIN 

 THEM, 



r.V PROFESSOR JAMES 1>. DANA. 



It has 1 < > 1 1 lt been recognized that the continent of North America has its 

 nucleal area of Archaean ruck- ; that the nucleal V has the same courses 

 in it- general outline as the continent ; and that then- are ranges of Archaean 

 ridges, more or less interruped, approximately parallel to the outline of the 

 V : among them, one along the Appalachian chain, and another along 

 much of the Rocky Mountain chain. Further, the positions of the ranges 

 of the Appalachians and the Rocky Mountains were, in 1875, made by me 

 the basis of a division of the continental surface into (1) an Eastern Border 

 region, east and northeast of the Green Mountain range; I 2) an Appalachian 



iuii, along the Appalachians west of the Archaean ranges from Alabama 

 to ( lanada, the Green Mountain area included : I •"> | an Interior ( Jontinental 

 basin, between the Appalachian chain and the Rocky Mountain chain ; and 

 (4) a Western or Pacific Border region, "west of the Rocky Mountain 

 Summit," as the four great partially distinct areas of continental progress, 



My subject at this time is: The areas of continental progress in the light 

 of existing facts, and the influence of their conditions on the work carried 

 forward within them. 



1. In the firsl place I observe that the boundaries separating the Atlantic 

 and Pacific borders from the Continental interior should he drawn, as far 

 as pos.-ihle, along the ranges of Archaean ridges jusl referred to. These 

 were boundaries al the beginning of Paleozoic time; and they have been 

 r Bince the more important division-lines for noting progress. On 

 account of the Archaean origin of these axial lines in the two mountain 

 chain-, and the fact that in their elevation the existence of the Appalachian 



and Rocky Mountain chain- had their beginning, I propose to Call each the 



Archaean protaxis of the chain. The Appalachian protaxis extends along 

 the Green .Mountain region as an interrupted range, and i> continued 

 through Putnam and Oran ( N < w York, northern New Jersey, 



eastern Pennsylvania, and thence southwestward to Georgia, as a series of 

 ridges, and in some parts nearly parallel ridges, making part of the wide 

 an a of crystalline rocks. 



The protaxis i- not now the highest part of the chain, but it i- the oldest 

 part ; and although an embryonic feature in the continent, it probably had 

 om >t throughout, which it has lost by time's long erodings. 



(6) 



