i894. CONTINENTAL GROWTH. 295 



been exposed to such long-continued denudation as the Appalachians 

 and Urals, for instance.^ 



Establishment of New Land-areas Connected with Mountain 



Upheaval. 



It is evident from the foregoing considerations that the establish- 

 ment of new land-areas, whether as continental additions or other- 

 wise, is closely connected with mountain upheaval : the two go 

 together. As I have shown, mountain ranges are never formed on 

 the sites of old denuded land-areas, they never arise in the middle of 

 a continent, but are always preceded by great sedimentation. An 

 old continent may subside in the middle or at the margin, and the 

 inland seas or other submerged areas receiving the sediment may in 

 process of time be upheaved vertically and folded horizontally by 

 lateral pressure, and so become eventually an integral portion of the 

 old land. In my "Origin of Mountain Ranges" I have sought to show 

 that this movement is due to expansion, the initial cause being the 

 heating of the sediments and undercrust by the rise of the 

 isogeotherms or surfaces of equal temperature brought about by the 

 accumulation of sediment. It is unnecessary to explain this principle 

 here, as it can be studied in the original work, but I am pleased to 

 point out that Mr. W. J. McGee adopts this theory in his "Memoir on 

 the Pleistocene History of North-East Iowa" (eleventh annual report 

 of U.S. Geol. Survey, 1889-90, pp. 351) with the suggestive 

 addition, since that the sediments rest on inclined surfaces and are 

 themselves inclined, the movement of expansion must have taken the 

 line of least resistance, and the expanding strata must have moved 

 seawards. '° Sedimentation, land-making, and mountain building, we 

 have every reason to believe, are directly related in the chain of cause 

 and effect. 



" "Contributions to the Study of Volcanoes," Judd, Geol. Mag., 1875, pp. 

 143-152. "The Geological History of some of the Mountain Chains and Groups 

 of Europe," Ramsay, Mining Journ., 1875. 



10 Mr. McGee says : — " The sediments of the successive mantles wrapped about 

 the young continent were dropped from the cold waters of deep ocean, and were 

 long chilled by contact with the waters ; yet by the end of the Silurian they were so 

 deeply buried as to no longer feel the chill waters, and to be heated by conduction 

 from the earth's interior ; and so the isogeotherms, or planes of equal temperature, 

 ose from the former ocean floor into and through the lower sediments, and their 

 temperature was greatly increased. As they were heated they expanded ; a part of 

 this expansion was vertical, and so peripheral portions of the continent were 

 elevated, not by the building up of successive sheets of sediment, but by their own 

 expansion ; yet a considerable part of the expansion must have been horizontal, and 

 must have resulted in either mass or particle movement, or both combined ; and 

 since the sheets of sediment rested on inclined surfaces and were themselves 

 inclined, the movement of expansion must have taken the line of least resistance, 

 and the expanding strata must have crept seaward, while the strata at some distance 

 from the shore line must have been compressed horizontally, perhaps buckled and 

 crumpled, and thrown into anticlinal and synclinal folds concentric with the shore, 

 or elsewhere crushed and broken into fragments along the planes of least strength." 



