70 



[No. 



separated by clays and sands. The Middle Headon is brackish 

 at the base but soon shows a marine fauna, 1 the Upper Headon 

 is a brackish and fresh-water formation. 



Above the Headon we have the Osborne beds, the most 

 unmixed fresh-water formation of the whole series. It is very 

 variable, but shows, in some places, 8—10 alternations: 2 sep- 

 tarian layers, 2 bands of ironstone and 6 horizons of concretionary 

 limestone with intervening clays and marls. 10 alternations 

 represent two oscillations and two arcs of the curve. 



The Bembridge stage covers the Osborne. First there is 

 a fresh-water building, the Bembridge limestone, which very 

 constantly shows three alternations of compact limestones with 

 clay and marl. The Bembridge limestone is covered by the 

 marine Bembridge Oyster-bed and close above this again there j 

 comes a layer of septarian stone, according to Forbes „very | 

 remarkable and constant." The Lower Bembridge marls succeed 

 with brackish and fresh-water fossils but without alternations j 

 and are covered by another layer of septaria sometimes sili- j 

 ceous, sometimes calcareous," and this divides between the 

 Lower and Upper Bembridge marls. In these Upper marls, j 

 which, like the Lower ones, contain brackish and fresh-water 

 fossils, indeed even lignites, I formerly thought there was evi- 

 dence of 4climaticalternations: there are 2 minor bands with pyrites, 

 one more marly bed, and at the top of the series a layer of 

 iron concretions covered with marl. But I now think it likely 

 that the marl and the 2 pyrite layers do not mark climatic 

 changes. If we only reckon with the ^remarkable and constant" j 

 septarian layers, then the Bembridge marls show only 3 alter- 

 ations o climate, and we should, thus, for the whole stage | 

 nave 6 climatic pe ri ods . The Bembridge s ^ C0DsequeD tly, j 

 one oscillation of the beach-line with 6 climatic alter- 



nations. 



Keeping *** 

 lere are 

 as of lot**' 



