934 GEOLOGY 



shelves have occasioned much discussion. 1 To the view that the 

 continental borders stood so high in recent times there are obvious 

 objections. One of them is the difficulty of disposing of the water 

 of the ocean when all the continents were lifted some thousands 

 of feet. Another is the fact that some of these valleys descend into 

 closed basins such as the deeper parts of the Mediterranean and 

 Caribbean seas and the Gulf of Mexico, which must be supposed to 

 have retained so much of their water as lies below the lowest notch 

 in their rims. 



The views of deformation here entertained afford a different 

 mode of interpretation, in which lateral movement plays a larger 

 part, and vertical movement a lesser part. This view cannot be 

 elaborated here, but some of its elements may be suggested. 



It is conceived that the continental protuberances, which stand 

 up some three miles, on the average, above the sea-bottom, may 

 have a movement somewhat akin to that of great ice-sheets, though 

 much slower, and that they tend to creep slowly out toward the 

 lower ocean basins. If such a movement took place, it would tend 

 to carry the valleys of the coastal lands out under the sea. It is 

 conceivable that the submerged valleys arose in this way. This 

 conception of the behavior of continental borders is too new to le 

 accepted without reserve, but if it is true, it helps to explain many 

 difficult problems connected with the coasts. 2 



However the submerged valleys originated, it seems remarkable 

 that they have not been filled with sediment, for the rivers must 

 have been carrying detritus, and littoral currents must have swept 

 drift into the channels. The efficient agent in keeping the valleys 

 unfilled was possibly the tides. Their ebb and flow, particularly 

 where the river-mouth broadened to an estuary, doubtless scoured 

 the channel, and not improbably enlarged and deepened it when- 

 the configuration of the surroundings favored. Tides would seem 

 to be especially effective in this work at the edge of the continental 



1 Spencer, Bull. Geol. Soc. Am., Vols. VI (pp. 103-140) and XIV 

 207-226); Am. Jour. Sci., Vol. XIX, 1905, pp. 1-15; and Am. Geol. XXIV. 

 1904, pp. 110-111; Hall, Trans. Victoria Inst., 1897 (pp. 30.1 324); ami I'.HHI 

 and 1902, and Geog. Jour., 1899; Nansen, Rep. Arc. Expl., p. '2:V2: Davidson. 

 Proc. Cal. Acad. Sci., Vol. I, 1897, pp. 73-103. 



2 For fuller statement of the hypothesis see the larger treatise of tin- 

 authors, Vol. Ill, pp. 519-530. 



