464 



REPORT OF NATIONAL MUSEUM, 1V>04. 



Such a work was necessarily largely a compilation and contained 

 little original matter. 



J. D. Dana, in an article On the Plan of Development in the Geo- 

 logical History of North America, called attention to the fact that the 

 greater mountain ranges border on the greater oceans in both Ameri- 

 cas, also to the apparent fact that volcanic activity, or 



Dana on the Plan of ' . i .1 . . 



Development of North at least the evidence ot the action of heat, was great- 

 America, 1856. 1 -1 • 



est along the coasts bordering on the greater oceans. 



Assuming that the typical form of a continent is a basin with bor- 

 ders of mountains facing the oceans, and the heights of the mountains 

 and volcanic activity are proportional to the size of the oceans, and 

 again that volcanoes characterize oceanic islands and not continental 

 interiors, he showed that the extent and position of oceanic depres- 

 sions have in a great degree determined the features of the land; that 

 oceanic depression and continental elevation have both 

 been in progress with mutual reaction from the begin- 

 ning of the earth's refrigeration. The original V-shaped 

 character of the North American continent he showed 

 to be due to the forces acting from the two oceans. 



" ( Ymtraction was the power, under Divine Direction, 

 which led to the oscillations of the crust, the varied suc- 

 cessions in the strata."'' These views, it will be observed, 

 are largely in accordance with those advanced in his 

 Wilkes Exploring Expedition report in 1849. 

 Prior to 1856 the age of the slates of Braintree, Mas- 

 sachusetts, had been problematical. By 

 most of the geologists of the time they 

 had been considered as Primary or, pos- 

 sibly, Transitional. A distinct advance was, therefore, 

 marked when, at the August, 1856, meeting of the 

 Boston Society of Natural History, Prof. W. B. Rogers 

 announced the finding in these slates of trilobites, later identified as 

 belonging to Barrande's Paradoxides and perhaps identical with 

 Green's Paradoxides harlcmi, which had been described from a speci- 

 men, source unknown, in the cabinet of Mr. Francis Alger. On 

 presentation of this evidence Rogers felt justified in referring the 

 Braintree slates to the horizon of the lowest Paleozoic group, or 

 about the level of the Primal rocks, the Potsdam sandstone, and the 

 Protozoic sandstone of Owen. The beds, it may be noted, are, in the 

 latest edition of Dana's Manual (1894), referred to the Middle Cam- 

 brian, and, therefore, lie below r the Potsdam. 



With the exception of the papers by Dana and Couthouy, scarcely 

 anything of consequence on the subject of corals, geologically consid- 

 ered, had thus far appeared from the pen of an American. At the 

 meeting of the American Association for the Advancement of Science, 



The Finding of 

 Paradoxides, 1856. 



Fig. 65. — Para- 

 doxides harlani. 



