ON THE MOVEMENTS OF THE EARTh's CRUST. 369 



earth is periodically variable in accordance with the eccentricity of the 

 orbit, these movements also take place periodically more rapidly and 

 more slowly. And as the sea always adjusts itself to the forces before 

 the solid eartb, it is probable that the shore-lines oscillate up and dt)wn 

 once for each rising and sinking of the eccentricity of the orbit. Tliis 

 applies both to the individual arcs of the curve and to the cycles. In 

 such a cycle " the mean level of the sea" rises and falls once during 

 sixteen oscillations. 



According to Darwin the sidereal day has become several hours 

 longer. It is therefore probable that so great a strain must have ac- 

 cumulated in the mass of the earth, that a slight increase of the strain 

 would suffice to effect cbanges of form at the weakest points. It is also 

 probable tbat these partial changes in tlie solid body of the eartb must 

 occur especially during great eccentricities, or some time after them, 

 when the motive power increases most rapidly. 



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 meters is sufficient to produce, 

 in the deeper basins, an alternation of many meters of thick marine atul 

 fresh-water deposits. And as regards the changes of the solid mass of 

 the earth, we must remember that the series of strata is not com[)lete 

 at any single place. In other words, the oscillations were not general 

 to such an extent as to render them contemporaneous 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 corresponding 

 to the arcs therefore can not be demonstrated everywhere, 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 ui)heavals may be consequent 

 u[)on 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 

 comparatively 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 pri?iciples in view, we compare the curve of the 



eccentricity with the geological series of strata, we find an agreenient 



which indicates that the hy[)0theses are correct. The two cycles of the 



calculated curve correspond to two geological cycles. Each of these 



H. Mis. 224 24 



