368 ON THE MOVEMENTS OF THE EARTH'S CRUST. 



mechanical sediments and the alternations of strata, so that without 

 taking these and perhaps other circumstances into consideration, we 

 can not prove the applicability of the hypotheses to the Palajozoic and 

 Mesozoic series. 



In conclusion, I will briefly notice the chief points in my hypothesis. 



The precession of the equinoxes and the periodical change in the eccen- 

 tricity of the earth's orbit, are reflected in the series of strata and furnish 

 the key to the calculation of the duration of geological epochs. 



Precession causes winter and summer to be alternately longer and 

 shorter. lu the semi-period when the winter is longer than the summer, 

 the diflerence between the inland and coast climate becomes more 

 marked. The atmospheric current becomes stronger. As a consequence 

 of this, the currents of the ocean increase in strength, and this again 

 re acts ou the climate. The periodical change of the climate caused by 

 precession is not very considerable, but still great enough to leave its 

 mark in the alternations of strata, and in the formation of shore-lines, 

 terraces, series of moraines, etc. One alternation of strata corresponds 

 to each precessional period. 



The eccentricity of the earth's orbit is periodically variable. Its mean 

 value rises and falls in periods of about 1,500,000 years, with sixteen 

 oscillations. Such a rise and fall I call a cycle, and each cycle, in the 

 calculated curve, is composed of sixteen arcs. 



The tidal wave, which is the most important agent in altering the 

 sidereal day, and which makes it longer, rises and falls to a certain ex- 

 tent with the eccentricity. It so predominates over the other forces 

 which alter the length of the sidereal day, that theday steadily lengthens 

 on the average more rapidly in the middle of the cycles when the mean 

 value of the eccentricity is greatest, and more slowly at the boundaries 

 between them, when it is least, and, as regards the individual arcs, 

 with increasing rapidity during rising, and decreasing rapidity during 

 falling eccentricity. 



The interior of the earth is i)lastic in consequence of the great pres- 

 sure. The surface or " crust," opposes the greatest resistance to change 

 of form. But as the sidereal day lengthens, and the equatorial parts of 

 the earth increase in weight, a constantly increasing strain acts out- 

 ward toward higher latitudes, and this strain increases until the re- 

 sistance is overcome. It must also be remembered that forces which 

 are too small to eflect any sudden alteration in a solid bodj^, may 

 nevertheless produce a change of form when they act for a long time. 



Hence the lengthening of the sidereal day does not act only upon the 

 sea, but also upon the form of the solid earth. The earth constantly 

 approaches more and more to the spherical form ; but the solid earth, 

 in its movements, lags behind the sea, which accommodates itself at 

 once to the altered time of rotation. 



As the motive power of these movements of the sea and the solid 



