342 



/. D. Dana on the Plan of Development 



Silurian strata (S S ; ) 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 Kocky Mountains and the 

 Pacific border, 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 strength of the forces at work. The force coming 

 from the Atlantic direction has left comparatively small traces 

 of its action at that time. Yet it has made its mark in the Azoic 

 stretching through Canada to Labrador, in the dip and strike of 

 the New York Azoic rocks, in the direction of the channel of the 

 St. Lawrence and the northwest coast of Lake Superior, and prob- 

 ably also in the triangular form of Hudson's Bay. Against this 

 primal area, as a stand-point, the uplifting agency operated, acting 

 from 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 appointed 

 functions in the plan of development, by wearing exposed rocks 

 and strewing the shores and submerged surface with sand, gravel 

 or clay, or else growing shells, corals and crinoids, and thus 

 storing up the material of strata and burying the life of succes- 

 sive epochs. y 



These long secular vibrations, movements by the age rather 

 than day, dipping the surface and raising it again in many and 

 varying 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 : 

 all would have been only a blank past. These forces, therefore, 

 working mainly from the southeast and southwest, were actually 

 organizing forces, essential to the completion of the continent, — 

 to the production of its alternations of limestones, shales, sand- 

 stones and conglomerates, and its sweeping catastrophes burying 

 the old preparatory for higher forms of life : — the continent in 

 the course of these movements, being at one time, it may be, 

 just beneath the ocean's surface, and having beds of sand and 

 gravel accumulating under the action of the waves ; then in some- 

 what deeper and clearer waters ; with limestones forming from 

 coral or crinoidal plantations or the growth of shells ; then, per- 

 haps, rising from the waves, bringing death upon its sea tribes 

 in one universal desolation ; then, sinking slowly in the waters 



