LIFE OF JAMES DWIGHT DANA 

 Development of the Earth 



" The grand outlines of Dana's system of the earth's 

 development are given in a few sentences in his article 

 ' On the Plan of Development in the Geological History 

 of North America,' first published in the American Jour- 

 nal of Science in 1856.* 



' What, then, is the principle,' he wrote, ' of develop- 

 ment through which these grand results in the earth's 

 structure and features have been brought about ? We 

 detect a plan of progress in the developing germ ; we 

 trace out the spot which is first defined, and thence follow 

 the evolution in different lines to the completed result: 

 may we similarly search out the philosophy of the earth's 

 progress ? The organizing agencies in the sphere are: 

 (i) Chemical combination and crystallization. (2) Heat, 

 in vaporization, fusion, and expansion, with the correlate 

 force of contraction which has been in increasing action 

 from the time the globe began to be a cooling globe. 



(3) The external physical agencies, pre-eminently water 

 and the atmosphere, chiselling and moulding the surface. 



(4) The superadded agency of life. Of these causes, the 

 first is the molecular power by which the material of the 

 crust has been prepared. The third and fourth have only 

 worked over the exposed surface. But the second, while 

 molecular in origin, is mechanical in action, and in the 

 way of contraction, especially, it has engaged the univer- 

 sal sphere, causing a shrinkage of its vast sides, a heaving 

 and sinking in world-wide movements. Its action, there- 

 fore, has been coextensive with the earth's surface through 

 the earth's history ' (loc. cit., p. 340). On a later page a 

 footnote again refers to this same dominant idea: ' I have 

 alluded on a former page to an analogy between the pro- 

 gress of the earth and that of a germ. In this there is 

 nothing fanciful ; for there is a general law, as is now 

 known, at the basis of all development which is strikingly 

 exhibited even in the earth's physical progress. The law, 



cial reference to American Geological History, for the use of colleges, 

 academies, and schools of science, by James D. Dana, pp. xvi.-ygS, illus- 

 trated by a chart of the world, and over one thousand figures, mostly from 

 American sources. Philadelphia and London, 1862. 



* American Journal of Science, Series II., vol. xxii., p. 339. 



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