510 A. Blvtt 071 the probable Cause of 



precessional period was also shorter. According to Geel- 

 muyden it would be very nearly proportional to the square of 

 the time of rotation. For example, to a rotation-time of 

 16 hours corresponds a (synodic) precessional period of 

 10,000 years, consequently only half the present period. The 

 shorter the period the less marked (other things being equal) 

 must the climatic period be, and the more indistinct the 

 alternation of the strata. 



Further, it must be remembered, that in Palseozoic and 

 Mesozoic times the moon was probably much nearer. In that 

 case the lunar tide was much stronger, and stronger in pro- 

 portion to the solar tide than at present The day was 

 shorter, and the stronger tidal wave acted more frequently. 

 The shores were more rapidly destroyed. Deposition, no 

 doubt, took place more rapid l3\ The sidereal day increased 

 more quickly in length than at present. All these circum- 

 stances must have had an influence upon the form of the 

 earth, upon the distribution of land and sea, upon the dis- 

 placement of shore-lines, upon the changes of climate, upon 

 the ocean-currents, upon the distribution of chemical and 

 mechanical sediments and the alternations of strata, so that, 

 without taking these and perhaps other circumstances into 

 consideration, we cannot prove the applicability of the 

 hypotheses to the Palaeozoic 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 eccentricity 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. In the semi-period when the winter is 

 longer than the summer, the diff'erence between the inland 

 and coast climate becomes more marked. The atmospheric 

 currents become stronger. As a consequence of this the 

 currents of the ocean increase in strength, and this again 

 reacts on 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, &c. 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^ million 

 years, w'ith 16 oscillations. Such a rise and fall I call a 



