1889.] THE DISPLACEMENT OF BEACH-LINES. 69 



arc 14 of the curve. This arc represents 100000 years and, 

 consequently, about 5 periods of precession. The Barton clay 

 is covered by the Headon sands, which show no alternations and 

 may have been formed in a comparatively short time. 



Between the Eocene and the Oligocene a great break exists 

 in the Isle of Wight. To this break, in the Paris basin, corre- 

 sponds the fresh-water Calcaire de St. Ouen. This is only 6—7 

 metres thick and shows 10 alternations of strata. Consequently, 

 according to my hypothesis, the Calcaire de St. Ouen ought to 

 represent about 200000 years. This would'seem to be a rather 

 long time for the forming of only 6—7 metres of limestone. 

 But it should be kept in mind, that, during the deposition of 

 these 6—7 metres of fresh-water limestone, the marine fauna 

 was radically changed. The Calcaire de St. Ouen divides be- 

 tween two geological formations, the Lower and the Upper 

 Tertiary. Of the Middle Headon marine animals, according to 

 the Quart. Journ. Geol. Soc, vol. 37, p. Ill, only one half to 

 one third belongs to Barton forms. And the Calcaire de St. 

 Ouen, probably, represents more than half of the interval that lies 

 between the marine beds of Barton and Middle Headon. Du- 

 ring the deposition of the Calcaire de St. Ouen no beds 

 were formed in the Hampshire basin which probably was then 

 not submerged in the sea. 



But the sea rose again and the Oligocene period commen- 

 ced. The first Oligocene stage, in the Isle of Wight, is the Lower 

 Headon, a fresh-water and brackish formation, showing one 

 oscillation of the beach-line. Marine shells (Cytherea, Mytilus) 

 sometimes occur in the middle beds of the stage, whilst the lower 

 and upper ones contain a fresh-water and brackish fauna. I have, 

 above, for this stage reckoned 7—8 alternations of strata. The stage 

 contains 5 limestone banks separated by clays and sands and 

 has, moreover, two horizons with iron concretions. It thus shows 

 7 alternations. 



The next stage or oscillation of the beach-line is represented 

 b y the Middle and Upper Headon. These have, together, 6 

 alternations, 4 limestones and 2 layers with iron concretions, 



