STRAND-LINE DISPLACEMENTS 475 



Yukonia. — Named for "the Yukon plateau. . . . The central area 

 may represent a positive element, the backbone of Alaska, compressed 

 between the thrusts from the Pacific and Arctic basins" (Willis, 1907, 

 397,398). 



Displacements of the Strand-line 



emergences and transgressions 



That the land moves up and down in causing the appearance and van- 

 ishing of seas is the widely accepted view of geologists, but that a sub- 

 mergence of the land may be due to a change in the hydrosphere without 

 the inundated land having moved at all is held by few. Dana, as long 

 ago as 1863, 111 called attention to the fact that an emergence of the land 

 may be due to a subsidence of the oceanic areas. He states: 



"As all parts of the earth, oceanic as well as continental, must have partici- 

 pated in the changes of level, the water-level was ever fluctuating like the land 

 level ; and hence it is not safe to measure the latter always by the former, as 

 is too commonly done. Many of the apparent elevations may have been due to 

 a deepening of the oceanic basin . . . and some of its apparent subsidences 

 may have been caused by an elevation of its bottom. It is probable that at 

 least 1,000 feet of the height of the continents . . . has arisen from the 

 increase in the depth of the ocean which took place during the successive Pale- 

 ozoic, Mesozoic, and Cenozoic eras." 



Suess has given a great deal of thought to the transgressions of the sea, 

 and has concluded that most of these can not be explained by subsidence 

 of the land. In his valuable work, Das Antlitz der Erde, the first two vol- 

 umes treat more or less directly of the movements of the lands and seas. 

 As his conclusions are of the greatest value in seeking for an explanation 

 of the various transgressions that have occurred in North America, it is 

 deemed necessary to introduce them here. The student, however, should 

 also consult the original work, which is now more accessible in the English 

 translation by Sollas and Sollas, entitled "The face of the earth." 



"It is usually assumed that the surface of the ocean is everywhere of equal 

 elevation, that is to say, that every part of it, and consequently every part of 

 its coast-line, is equally distant from the center of the earth. But this assump- 

 tion . . . can not be maintained. ... It must be considered as proved 

 that the mass of the continents exerts a considerable attraction upon the 

 ocean and that consequently the surface of the sea rises toward the mainland. 

 . . . The difference of elevation in meters amounts, according to Fischer, to 

 about 122 times the difference of the number of oscillations of the pendulum in 

 twenty-four hours. This would give, with a difference of nine oscillations, for 

 example, between an oceanic island and the coast, an actual difference in ele- 



111 Dana : Manual of Geology, 1863, p. 723. 



