MIDDLE TERTIARY. 175 



leading to the conclusion that the upheaval of 



the chalk, which now runs in a nearly vertical 



sition through the Isle of Wight, had alreadv 



in to supply the calcareous matter, which the 



»ams brought into the lakes of the Headon 



period. 



The beds which rest upon the Upper Headon 



strata are termed the Osborne or St. Helen's series. 



They are sandstones and marls, much thicker 



than any of the sandstones and maris in the 



Headon beds, and therefore m contrast to them. 



sandstom me calcareous, and 



>s into concretion- 



The 



shells are all of I 

 water tyj - 



sand- - une- 



times ripple - ma 



. by the wind. 



( tsbon 



about Sc ^K$*tf<35?V • ^ 



thick, and divide the ^it^^l* 



I [eadon from the Bern- " I J 



bridge beds. Tin ^^^■S^^P^^ 



. / ,- } i<;. i& I'lainTbi^ i-imniphalus and 



the fcsh-water 

 thick, very like the Headon limes! 



Headon limestones, 



rather creamy in colour, full of the same types 

 of fresh-water shells, and containing many land 

 shells, especially examples of the genera Helix, 



Bulimus % and Glandifta. These land-shells have a 

 marked affinity with species now living in North 

 America, with which one or two may be identical. 

 The Bembridge limestone abounds in seed-vessels 

 of the plant Chara, which formed it. Remains 

 occur in it of several species of the extinct mam- 



\ 



