ON THE MOVEMENTS OF THE EARTh'S CRUST. 371 



water of the river was purer, aud chemically formed beds bad time to be 

 deposited. Instead of clay and marl, — limestone, Septaria beds, iron- 

 stone, etc, were formed. These beds were undoubtedly formed much 

 more slowly than the sand, clay, and marl" deposits which alternate 

 with them. They are analogous to the forest beds in peat-mosses. 

 Forest beds often separate i)eat deposits with diiferent species of plants. 

 This shows that the forest beds indicate long dry periods, during which 

 the formation of peat ceased and the Hora became changed ;* when the 

 quantity of rain again increased and the formation of peat commenced 

 anew, the Ibrest trees which grew around the mosses were changed, and 

 the forest beds thus make divisions between different sub-stages or zones 

 in the i)eat. 



Among the beds deposited in water (whether fresh or salt-water for- 

 mations) it is chiefly the above mentioned cheuiically formed beds that 

 are formed in dry periods. Aud just as in the peat mosses forest beds 

 often separate peat deposits with a different flora, so liinestone aud 

 Septaria beds also fre<iueutly intervene between clay, marl, and sand 

 deposits with a more or less different fauna, so that these chemicall}^ 

 l)roduced deposits often form boundaries between geological stages and 

 sub-stages. This is the case, for example, in the Fluvio-marine series of 

 the Isle of Wight, the main features of which we shall now pass on to 

 describe with the aid of Forbes's detailed and classical statements. We 

 shall then see that we have fewer climatic changes than I previously 

 supposed, and that the series of beds in the Isle of Wight coincides as 

 admirably with the curve of eccentricities as the Parisian deposits, 

 although somewhat later on in time than was hitherto supposed; thus 

 the agreement with the palieontological results becomes complete. 



We begin from below, with the Ui)per Eocene Barton Clay. Judging 

 from the fossils this is synchronous with the Gres de Beauchamp in 

 the Paris Basin. It has five Septaria beds, and corresi)on<ls to arc 14 

 of the cnrve, which has the same number of precessional periods. The 

 Barton Clay is covered by the Headon ^ands (previously referred to the 

 Upper Bagshot), which have no alternations, aud which were probably 

 formed in a comparatively short time. 



A great gap now follows in the series in the Isle of Wight. In the 

 Paris Basin the freshwater Calcaire de St. Ouen was formed at this 

 time. This is only to 7 meters thick, but it has ten alternations, which 

 should represent 200,()()() years according to my calculation. It might 

 seem that this was a long time for the formation of a stage of so little 

 thickness; but while this stage was deposited the marine fauna was 

 changed to such an extent that a great geological boundary has been 

 drawn through this point, the boundary between the Eo(;ene and Oligo- 

 cene. The first marine Oligocene bed in the Isle of Wight (the Marine 

 Headon) has a fauna of which only 30 to 50 per cent, of the species 



* See "Tlieori oin liul vimd' higiMi af NorgoH Flora under vekslende regiil'uldc o 

 t^rre Tider," iu Nyt Mag, for Natt^rv.) 187(5, xxi, (pp. 52, 53 of separate copies), 



