100 J. D. Dana on the Origin of Continents. 
era. The dip of the new red sandstone accompanying them is 
probably another effect. ‘The Ozark mountains, forming a line 
parallel with the Appalachians, beyond the Mississippi, may be 
referred to the same system of changes. 
The economical advantages belonging to the features of North 
America that have thus originated, are most remarkable, and 
this view of their origin gives them increased interest. The 
Silurian rocks indicate that before the coal period the region was 
comparatively level, and lay. mostly beneath the sea. As it 
emerged it was still dripping with water, so that, under a climate 
peculiarly genial, coal vegetation might have grown luxuriantly. 
But had it continued thus flat to a later period, it would have had 
but small streams, and probably, for want of a mountain barrier 
to intercept the drying Pacific winds, the desert regions of the 
west would have traversed the land, as Sahara has spread over 
Africa. As if to prevent these results, and give a vastness scarcely 
equalled to its resources, the land was raised into mountains 
on either coast, those of the west, where the barrier was most 
needed, ascending even to the regions of perpetual snows. The 
whole interior is now enclosed by the Rocky Mountains on the 
one side and the Appalachians on the other, and a thousand 
streams are set in motion over the wide land from either bound, 
all to contribute to a common trunk, the great highway of the 
country. ‘Thus the largest possible extent of intercommunicating 
inland waters has been secured; and for the same reason a great 
rt have been made to flow so nearly on a plain as to afford navi- 
gation almost from one end of the territory to the other, and extend 
their fertilizing influence over the whole surface. A similar result 
has been produced on the narrow ocean side of the main chains by 
been 
compelled to flow far north and south between these ranges, 
and fertilize an extended country before the sea was reached. 
Thus the noble Columbia, with its wide spread tributaries, was 
made for Oregon ; and in the same manner were formed the Wil- 
lammet, the Sacramento, and the Joachim, which run in long - 
courses between the Cascade and Coast ranges of heights. Thus 
on the Atlantic side, we have the Shenandoah and other head 
waters to the Potomac, and at the north, a Hudson, Connecticut 
and Merrimack flowing in parallel lines. 
_Note.—In connection with this article, it should have been ear- 
lier mentioned that the theory of “ secular refrigeration” has been 
presented with much force, in many points of view, by W. W. 
Mather, in this Journal, vol. xlix. p. 284, (1845), and the foldings 
of the Appalachians are attributed by him to this cause, ! 
