512 A. Blytt on the probable Cause of 



The change in the tidal wave with the eccentricity is 

 supposed to be sufficiently great to explain the displacement 

 of shore-lines. A vertical displacement of the shore-line by 

 a few metres is sufficient to produce, in the deeper basins, an 

 alternation of many metres of thick marine and freshw^ater 

 deposits. And as regards the changes of the solid mass of 

 the earth, we must remember that the series of strata is not 

 complete at any single place. In other words, the oscillations 

 were not general to such an extent as to render them con- 

 tempoi'aneous everywhere. It is only by partial changes of 

 form, sometimes here, sometimes there, at those points which 

 were weakest at each period, that the solid earth has approached 

 the spherical form. To each arc of the curve, therefore, there 

 corresponds only a partial, not a general, alteration of the form 

 of the solid earth. And the oscillation of the shore-lines corre- 

 sponding to the arcs, therefore, cannot be demonstrated every- 

 where, but only in the basins where the forces at the time 

 exerted their action. Hence we can only obtain a complete 

 profile by combining the beds of all the Tertiary basins. 

 Nor were the changes of the solid earth everywhere equally 

 great, but they were greatest at the most yielding parts of 

 the surface, so that very considerable local upheavals may be 

 consequent upon small changes in the length of the sidereal 

 day. This applies to the individual oscillations ; but even the 

 great overflows of the sea of which one falls in each cycle 

 need not be due to any very great rise in the level of the 

 sea, for great plains may be flooded and drained by a com- 

 paratively small vertical displacement of the shore-line. But 

 these great changes in the distribution of land and sea were 

 undoubtedly great enough to cause considerable alterations of 

 climate. Great seas in high latitudes render their climate 

 mild, and vice versa. 



If now, keeping these principles in view, we compare the 

 curve of the eccentricity with the geological series of strata, we 

 find an agreement which indicates that the hypotheses are 

 correct. The two cycles of the calculated curve correspond 

 to two geological cycles. Each of these cycles has 16 arcs, 

 which correspond to 16 smaller oscillations of the shore-lines, 

 or 16 geological stages. In each of these stages there are as 

 many alternations of strata as there are precessions in the 

 corresponding arc. And the " mean sea-level " rises with the 

 mean eccentricity in the middle of the cycles, and falls at the 

 boundary between them, and hand in hand with the mean sea- 

 level the temperature in the higher latitudes also rises and 

 falls. 



The theory here discussed agrees with LyelFs great 



