344 J.D. Dana on the Plan of Development 
oscillations, causing submergences, for these continued long to 
occur; but the gain, on the whole, was a gain—a progress; and 
the moving ages made the accession a sure and permanent gain 
as the continent became more stable. 
II. But in the statement that the growth of the continent was 
to the south, southeast, and southwest, we assert only the most 
general truth respecting it. The continent has its special features 
as much as any being of organic growth, and the elimination of 
these features is to be traced to the same system of forces. e 
Appalachian range on the east, the Rocky Mountains and the 
subordinate chains on the west, the lower lands and lakes of 
the interior, all in systematic relation, are the more marked of 
these features; and the vast river systems, with the broad allu- 
vial flats and terraced plains, the wide spread drift, the denuded 
heights and channeled slopes and lowlands, are subordinate pe- 
culiarities of the face of ‘he continent. 
ry 
the future of the continent, its low centre and high borders, was 
sempre We can hardly doubt that the region of the 
te a ot 
after the appearance of the Azoic nucleus, there were two prom- 
inent lines of development; one along the Appalachian region, 
the other along the Rocky Mountain region—one, therefore, pat 
allel with either ocean. ndward, beyond each of these devel- 
oping areas, there was a great trough or channel of deeper ocean 
waters, separating either from the Azoic area. 
* Address dc.—See this volume, page 319. 
