342 J. D. Dana on the Plan of Development 
— strata (SS;) but it is itself free from superincumbent 
beds, and therefore, even in the Silurian age, it must have been 
above the ocean. And ever since, although subject, like the 
rest of the world, to great oscillations, it has apparently held its 
place with wonderful stability, for it is now, as probably then, 
not far above the ocean’s level. 
This area is central to the continent; and, what is of promi- 
nent interest, it lies parallel to the Roe ky Mountains and the 
acific bo rder, thus proving that the greater force came from 
~ that direction in Azoic times, as well as when the Rocky Moun- 
tains were raised. Thus this first land, the germ or nucleus of 
the future continent, bears in itself evidence with respect to the 
direction and stren ngth of the forces at work. The force coming 
from the Atlantic 
seretching through Canada to reior, in ie dip and strike of 
the New York Azoic rocks, in the direction of the channel of the 
| anor ce and the northwest coast of Lake Superior, and prob- 
aby also in the triangular form of Hudson’s Bay. Against this 
a area, as a stand-point, the uplifting agency operated, acting 
om the two directions, the Atlantic and the Pacific; and the 
evolution of the continent took place through the consequent 
vibrations of the crust, and the additions to this area thereby 
resulting; the ocean in the meantime pursuing its appoint 
fanctions in the plan of development, by wearing exposed rocks 
and cae the shores and ith 
or clay, or else growing shells, corals and crinoids, an 
storing up the material of strata and burying the life of succes- 
sive € 
These long secular vibrations, movements by the age rather 
than day, dipping the surface and rai sing it again in many an 
ere successions, were absolutely essential to the progress. 
Had the continent been stable, there could have been no history, 
no recorded events of changing life and alternating deposits: 
gravel pepe ate under the me of the waves; then in mie 
haps, rising from the waves, ad death upon its sea 
in one universal desolation ; then, sabi slowly in the waters 
’ * 
