404 E. (). ULRICII REVISION OE TJIE I'vVLEOZOIC SYSTEMS 



are being ascribed chiefly to changes in or beneath the hydrosphere itself 

 without vertical movement in the land. That the latter view is more 

 nearly right than the former can not be denied. Keither can it be de- 

 nied that most of the great sea withdrawals, also many of the minor 

 withdrawals, were immediately and chiefly occasioned by deepening of 

 the permanent oceanic basins or by some other condition inducing nega- 

 tive fluctuation of the water level independent of land movement. But 

 these changes within the hydropsphere were perhaps only seldom or never 

 solely responsible for the migrations of the strandline. If the deepening 

 of the oceanic basins was a broad synclinal effect of the shrinkage of the 

 lithosphere, then we may for equally good reasons assume a contempo- 

 rary anticlinal effect on the continents that must have contributed in a 

 small or larger degree to the conditions causing general sea withdrawal. 

 After all, then, displacements of the strandline are always connected 

 with some body deformation of the earth. 



As to the alternating withdrawals and transgressions of the sea, these 

 seem to have occurred, at least in Paleozoic times, much more frequently 

 than even Suess conceived. The diagrams on pages 346 and 347, illus- 

 trating invasions of seas, give a generalized idea of these migrations of 

 the shore; but the presentation is confessedly inadequate in the matter 

 of number and detail. To what extent land deformation contributed to 

 the production of these broad migrations perhaps can not be definitely 

 determined. Sea filling, continental attraction, deepening of oceanic 

 basins, and the equatorial heaping of waters incident to accelerated rota- 

 tion of the earth about its axis at times of pronounced shrinkage, the last 

 suggested by Suess and more recently by Schuchert (Bull. Geol. Soc. 

 America, vol. 20, p. 505) as possibly important, are all forces or pro- 

 cesses that may have operated concomitantly or separately in producing 

 displacements of the strandline. The forces being in part compensatory, 

 the advance or retreat of the waters, as the case may be, is the^ resultant 

 of their variant activities. A¥hile the competence of these various fac- 

 tors to effect general submergence or emergence is admitted, it is denied 

 til at this fact necessarily excludes the operation of deformative move- 

 ments within any part of the land-masses themselves. 



That the marginal areas of the continents were at times elevated and 

 folded is, of course, accepted by all — even by Suess and his followers, 

 who speak of the continents as having the character of "horsts" and of 

 the ocean basins as being permanently "sunken areas." This authority, 

 however, tends to the belief or conviction that the median areas of the 

 continents are essentially stable, a conviction shared and recently ex- 

 pressed by Schuchert, who holds "that the continent (North America) 



