1889.] THE DISPLACEMENT OF BEACH-LINES. 83 



fresh. In such deep basins, consequently, slight displacements of 

 the beach-line may lead to an alternation of thick fresh- and 

 salt-water layers, and all such alternating beds may even be 

 deep-water formations. 



The shifts of the sea-level, indicated by the geological stages, 

 were thus probably only very small. 



And the great upheavals and subsidences are caused by 

 strains which have accumulated through very long periods. 

 In Postglacial times great parts of the continents in higher 

 latitudes have been considerably upheaved. The terraces 

 and raised beaches tell that. In Norway, the highest marine 

 terraces are found as high as 188 m. above the sea, but this is 

 the case only in some places; usually they lie much lower, and we 

 would get a much lower figure, if we were to give the mean value of 

 the rising for the whole peninsula. In Arctic North America, 

 there are in some places marine traces up to 550 m. above the 

 § ea, but also here the mean value would be much less. If, now, 

 « could be shown that such great and extensive upheavals were 

 common, in the course of time, the hypothesis would no doubt be 

 Jt 8 lnsuffici ent to explain the facts. But the fact is that such 

 ^eavals are of rare occurrence. They only take place now 

 chin t6r the lapse of ver y lon g Periods. It is such great 

 vide t S m geographical condi tions, which enable us to di- 



camol. mT ge ° l0giC CyClGS ' and they result from strains ac - 

 of tim" lengthenin g of sidereal day through periods 



is rele C ' rre8pondin « to whole cycles of the series. When that 

 hvnoth 6 " 1 Gred We may ' P erha P s > feel more confident that the 

 "Wthesis is probable. 



^ th T S6e ' Whether the h yP° the sis has at its disposal, 

 is impos s i h r"? UffiCient t0 account for the chan ges observed. It 

 do not kno > GVer ' t0 makG a definite calculati ™> ^eause we 

 tidal fri cti ° W Speed at wbich the sidereal day is lengthened by 

 Let us T' We ° nlj kn ° W that ft is Ien gthened very slowly. 

 Sir ^iUiaTrT ValUe ° f tidal retardation > as calculated by 

 omsan experimentally, to be a probable one. The 

 according to that calculation, the rotation 



Uc Wde retards, 



