286 UPPER EOCENE FORMATIONS. [Ch. XVI. 



Many of the marine shells of the blackish-water beds of the above 

 series, both in the Isle of Wight and Hordwell Cliff, are common to 

 the underlying Barton Clay ; and, pn the other hand, there are some 

 freshwater shells, such as Cyrena ohovata, which are common to the 

 Bembridge beds, notwithstanding the intervention of the St. Helen's 

 series. The white and green marls of the Headon series, and some 

 of the accompanying limestones, often resemble the Eocene strata of 

 France in mineral character and color in so striking a maimer, as to 

 suggest the idea that the sediment was derived from the same region, 

 or produced contemporaneously under very similar geographical cir- 

 cumstances. 



At Brockenhurst, near Lyndhurst, in the New Forest, marine strata 

 have recently been found, containing fifty-nine shells, of which many 

 have been described by Mr. Edwards. These beds rest on the Lower 

 Headon, and are considered as the equivalent of the middle part of 

 the Headon series, many of the shells being common to the brackish- 

 water or Middle Headon beds of Colwell and Whitecliff Bays, such as 

 Cancellaria mitricata, Sow., Fusus labiatus, Sow., &c. Baron von 

 Konen * has pointed out that no less than forty-six out of the fifty-nine 

 Brockenhurst shells, or a proportion of 78 per cent., agree with species 

 occurring in Dumont's Lower Tongrian formation in Belgium. This 

 being the case, we might fairly expect that if we had a marine equiv- 

 alent of the Bembridge series, or of the contemporaneous Paris 

 gypsum, we should find it to contain a still greater number of shells 

 common to the Tongrian beds of Belgium, but the exact' correlation 

 of these freshwater groups of France, Belgium, and Britain, has not 

 yet been tally made out. It is possible that the Tongrian of Dumont 

 may be newer than the Bembridge series, and therefore referable to 

 the Lower Miocene, according to the classification adopted by me in 

 Chapter XIV. p. 217. 



If ever the whole series should be complete, we must be prepared 

 to find the marine equivalent of the Bembridge beds, or the upper- 

 most Eocene, passing by imperceptible shades into the overlying 

 lowest Miocene strata. 



Among the fossils found in the Middle Headon are Cytherea in- 

 crassata and Cerithium plicatum, fig. 173, p. 240. These shells, espe- 

 cially the latter, are very characteristic of the Lower Miocene, and 

 their occurrence in the Headon series has been cited as an objection 

 to the line proposed to be drawn between Miocene and Eocene. 

 But if we were to attach importance to such occasional passages, we 

 should soon find that no lines of division could be drawn anywhere, 

 for in the present state of our knowledge of the Tertiary series there 

 will always be species common to beds above and below our boundary- 

 lines. 



Both in Hordwell Cliff and the Isle of Wight, the Headon beds 



* Quart, Geol. Journ., vol. xx. p. 97. 1864. 



