J. D. Dana on the Plan of Development, fyc. 335 



Art. XXT. — On the Plan of Development in the Geological His- 

 tory of North America, with a map ; by James D. Dana. 



On other occasions, I have discussed at some length, the out- 

 line and surface features of the continents, the parallel courses 

 of island groups, and the relations between the structure of the 

 continental borders and the extent of the adjoining oceans ; and 

 I have endeavored in connection to elucidate the great principle 

 of geological dynamics, which is at the basis of these character- 

 istics of our globe.* I propose at this time to point out the rela- 

 tions between the operations of this principle or agency and the 

 special geological history of the North American continent. 



To render this application of the subject intelligible, it is ne- 

 cessary to review briefly the fundamental facts just alluded to. 

 For this purpose, I would direct attention to a Mercator's Chart 

 of the World, (see plate) on which the whole is open to exami- 

 nation — such a chart being a minature representation of the facts 

 themselves, and the order observed among its parts, the syllables 

 which spell out the principles. 



In the first place, note the two great oceans, the Alantic and 

 the Pacific — 'both widening south, and coalescing in a vast ring 

 of ocean around the south pole, while narrowing north and uni- 

 ting in a small arctic sea. The Indian Ocean is a third north 

 and south ocean : but it reaches north only a little ways beyond 

 the equator. 



As the Atlantic is less than half the breadth of the Pacific, so 

 the American continent is less than half the breadth of the great 

 Orient, including Europe, Asia and Africa. It is seen also that 

 while the North Atlantic treads off to the northeast, and the 

 whole Atlantic is a zigzag channel with a main northeast course, 

 the Pacific is a northwest channel, its longest diameter (repre- 

 sented by the line M M), being at right angles nearly with the 

 trend of the Atlantic (N 1ST). This longest diameter, moreover, 

 corresponds with the general trend of the Pacific islands ; for 

 these islands have a nearly parallel course all through the ocean, 

 the New Hebrides, Kingsmills, Samoan, Tahitian, Marquesas 

 and Sandwich islands, lying in approximately parallel lines.f 



* Am. Jour. ScL, [2], ii, 335, 352, iii, 94, 176, 381, iv, 88 ; Report, Geol. Expl. Ex- 

 ped., 756 pp. 4to., 1849, pp. 11, 414, 429 ; Proceedings Amer. Assoc. vol. ix, Provi- 

 dence Meeting, 1855, and page 305 of this volume. 



f I may here add, what I have elsewhere explained at length, that the trends of 

 the Pacific, while having a general correspondence of direction, pertain to two sys- 

 tems, one the Central Pacific, the other the Australasian. The Central Pacific begins 

 in the Paumotu Archipelago, or rather still farther east, in Easter Island and Gomez ; 

 is thence continued on a west-northwest course, by the Society Islands, and the Her- 

 vey Islands more south ; thence by the Samoan and Fakaafo groups ; thence more 

 northwesterly by the Vaitupu and Kingsmills, to the Radack and Ralick groups, 



