OSCILLATION, PERMANENCE, GROWTH. 187 



through the transfer of masses by erosion and sedimentation, for that 

 hypothetic process is essentially conservative. Neither is it easy to be- 

 lieve that the two margins of the plains have differed, since the Creta- 

 ceous, to the extent of one mile in their radial contraction due to secular 

 cooling of the globe ; nor is it easy, at least for the disciple of isostasy, to 

 believe that such a change can have resulted from the localization of 

 deformation consequent on the slowing of the earth's rotation. Each of 

 these processes may have been concerned, but I conceive that the essen- 

 tial factor still awaits suggestion. Our knowledge of surface processes, as 

 compared to subterranean, is so full that the field of plausible epigene 

 hypotheses may be exhausted, but the vista of hypogene possibility still 

 opens broadly. 



Are Continents permanent ? — The doctrine of the permanence of the con- 

 tinental plateau, enunciated long ago by Dana and more recently advo- 

 cated, with a powerful array of new data, by Murray and Wallace, has 

 made rapid progress toward general acceptance. Nevertheless its course 

 is not entirely clear, and among the obstacles still to be overcome is one 

 whose magnitude is perhaps magnified for the American student by prox- 

 imity. All who have studied 1 iroadly the stratigraphy of the Appalachian 

 district have concluded that the sediments came chiefly from the east; 

 and the detailed Appalachian work of the past decade is disclosing a 

 complicated history, in which all chapters tell of an eastern paleozoic 

 land, and some chapters seem to testify to its wide extent. At some 

 times the western shore of this land lay east of the site of the Blue Ridge, 

 and there is serious doubt whether the existing belts of coastal plain and 

 submerged continental shelf afford it sufficient space. For the present, 

 at least, the subject of continental permanence must be classed with the 

 continental problems. 



Do Continents grow? — According to my own view, there is yet another, 

 a sixth, continental problem deserving the attention of the World's Fair 

 intercontinental congress. We have been told by the masters of our 

 science, and their teaching has been echoed in every text-book and in 

 every class-room, that through the whole period of the geologic record 

 the continents have grown ; not that the continental plateaus have been 

 materially extended, not that the pendulum has moved always in one 

 direction, but that the land area has, on the whole, steadily increased. 

 From this doctrine there has been no dissent — and possibly there should 

 be no dissent — but the evidence on which it is founded appears to me so 

 far from conclusive that I venture to doubt. 



The evidence employed consists partly in the general distribution of 

 formations as shown by the geologic map and partly in inferences drawn 

 from certain formations which contain internal evidence that they orig- 



XXVIII-Bull. Geol. Soc. Am., Vol. 4, 1892. 



