158 GEOLOGY OF THE ISLE OF WIGHT. 



Not only is this horizon noticeable for the occurrence in it of 

 shoals of small fish and prawns, but the abundance of scales and 

 vertebrae of the ganoid Lepidosteus is of great interest. A bed 

 which yields such well-preserved fish and prawns is likely also to 

 contain plant-remiiins and insects. A few plants have already 

 been obtained from it near Ryde. During a recent visit to 

 Cliff" End numerous well-preserved plants were discovered on 

 this horizon (by Clement Pieidand Henry Keeping). No attempt 

 was then made at systematic collecting, but during an hour or 

 two's search grass or sedge-like leaves of several genera, palm ?, 

 fern, and fragments of several peculiar reticulated leaves were 

 found. This locality would repay more minute examination, as 

 scarcely anything is yet known about the botany of the Osborne 

 period. 



Bembridge Limestone. 



Of the Fluvio-marine strata of the Isle of Wight, the Bem- 

 bridge Group is by far the most constant in lithological characters, 

 and the changes exhibited by its component strata throughout 

 their range are for the most part slight and unimportant. It 

 is consequently everywhere easily recognizable by mineral com- 

 position, and, as might be expected, its most characteristic fossil 

 contents are, in the main, very uniformly distributed. Its lower 

 portion is most calcareous, and everywhere in the Island exhibits 

 more or less compact limestones, occasionally separated by shales, 

 and accompanied by marly beds. 



These limestones in the first edition of the Map and Memoir 

 were treated merely as part of the Bembridge Series. But it has 

 been found easy to separate them on the more accurate topographical 

 map now available, for they form the most marked feature to be 

 seen in any bed above the Chalk in the Island. There is also in 

 places a distinct line of erosion between them and the overlying 

 marls, and everywhere proof may be found of a sudden break and 

 change in the conditions of sedimentation, from an almost purely 

 calcareous freshwater deposit, to a marine clay or sand. 



As there is an equally sharp line at the base of the limestone, 

 where it rests on the mottled clays of the Osborne Series, the 

 Bembridge Limestone is here treated as a separate subdivision, not 

 necessarily differing greatly in age from the older or newer 

 deposits, but showing a marked change of physical conditions at 

 the time of its formation. 



The Bembridge Limestone includes the uppermost limestones of 

 Headon Hill and Sconce, and the well-known limestones of Ham- 

 stead and Gurnard Ledges, Cowes, and Binstead. On the same 

 horizon lies the rock which, owing to a dip slope, spreads over so 

 wide an area near Wellow and Newbridge. 



Headon Hill. — This important member o£ the Isle of Wight 

 Tertiary series plays but an inconspicuous part in the Headon 



