STRAND-LINE DISPLACEMENTS 479 



"Material is continually being carried into the sea. . . . The oceanic 

 regions are filled up slowly but without intermission, and their waters in con- 

 sequence are gradually displaced" (II, 540-543). "Every grain of sand which 

 sinks to the bottom of the sea expels, to however trifling a degree, the Ocean 

 from its bed" (II: 555). 



"The formation of sediments causes a continuous, eustatic positive movement 

 of the strand-line. 



"We are thus acquainted with two kinds of eustatic movement ; one, pro- 

 duced by subsidence of the earth's crust, is spasmodic and negative ; the other, 

 caused by the growth of marine deposits, is continuous and positive" (II : 543- 

 544). 



In regard to the traces of the elevated horizontal shorelines occurring 

 along most modern coasts, Suess states that 



"the more recent movement was an accumulation of water towards the equator, 

 a diminution toward the poles, and as though this last movement were only one 

 of the many oscillations which succeed each other with the same tendency, 

 i. e., with a positive excess at the equator, a negative excess at the poles" 

 (11:551). 



In conclusion, Suess says : 



"In all probability the Ocean is subject to an independent movement which in 

 the course of long periods causes an alternation of positive and negative phases 

 at the equator. We shall be able to discuss this oceanic movement with greater 

 certainty when the stratified series in high latitudes is better known, and when 

 we are able to clearly distinguish the terraces formed by glacial lakes from 

 those of marine origin. These great oscillations are not, however, cumulative 

 in time ; on the contrary, they are compensatory. The persistent continuance 

 of a continental surface is in the main the result of local subsidences of the 

 earth's crust, which time after time open up fresh abysses for occupation by 

 the sea, and lower the general level of the strand. Every eustatic negative 

 movement of this kind . . . induces a heightened eustatic positive move- 

 ment. . . . The effect of eustatic subsidences and the deposition of sedi- 

 ments is cumulative, and in the course of geologic periods the eustatic negative 

 movements obtain the predominance. In this matter the folding of the moun- 

 tain chains plays only a secondary part" (II : 553). 



PALEOZOIC EMERGENCES AND SUBMERGENCES 



General discussion. — From the preceding pages it may be learned that 

 there are periodic recurrences of extensive emergences of the continents 

 and that each one is later invaded or transgressed by continental seas of 

 greater or less extent. The emergences mature far more rapidly than the 

 transgressions. The former are thought to be due to the periodic sub- 

 sidences of the oceanic bottoms, while the cause of the transgressions is 

 not so clear. It is concluded, however, that the unloading of the com- 

 bined continents into the seas is of primary importance in this connection. 



