TEANSACTIONS OF SECTION C. 515 



The gravel beds, which rest upon the older Tertiary strata, whether the oldest or 

 higher level gravels, or the newer, siicli as those which occupy the comhes and 

 transverse valleys, are unnifected by these movements, showing that their origin is 

 subsequent to the disturbing forces which affected the Secondarv and Tertiary rocks 

 below them or on which they rest. 



LoAVER Tertiakt Strata of the Isle of "Wight. 



The Lower and Middle Eocene strata of the Isle of Wight, especially up to the 

 base of the fluvio-marine series, may be better studied in the cliffs m Alum Bay and 

 Whitecliff Bay than in any other part of the island. 



In these remarkable sections the whole of the strata from the chalk to the fluvio- 

 mariue formation are displayed in unbroken succession. 



Plastic Clay. 



' The lowest member of this group of strata in the Isle of Wight is the Plastic 

 Clay, or Woolwich and Reading series of Mr. Prestwich.' These beds are best ex- 

 amined in Whitecliff Bay and Alum Baj-, especially the former, where the mottled 

 beds are well exposed. No fossils have'occurred in the plastic clay of the island. 

 Seven beds have been recognised, the whole measuring So feet ; they constitute a 

 narrow belt striking across the island, resting on the chalk. 



The London clay succeeds the plastic clay, and also forms a narrow belt extending 

 across the island from the west coast at Alum Bay to the east at Whitecliff or 

 Culver Cliff; its thickness is about HOO feet. A baud of flint pebbles only 2 inches 

 thick diA-ides the plastic clay from the London clay, representing the basement bed 

 of Mr. Prestwich. Nowhere in Britain can the London clay be so advantageously 

 studied as at Whitecliff Bay, or where the characteristic fossils are better exposed. 

 Twenty-five to thirty characteristic species may be collected here. Amongst others 

 may be named Pinna affinis, Pectimculus hrevtrostris, I'holadomya margaritacea, 

 Panopea intermedia, and Modiola elegans. The annelide Bitrupa 2}lana belono-s 

 essentially to the London clay. 



Middle Eoceke. 

 Lozver Bcif/shot Beds. 



Joshua Trimmer, in 1850, first applied the term Bagshot to the whole series of 

 strata in Alum Bay and Whiteclifl" Bay, dividing it into upper, middle, and lower, 

 thus correlating it with the corresponding series in the London area which had' 

 been previously established by Professor Prestwich. 



The Lower Bagshot beds are greatly developed in the Isle of Wight, attaining 

 a thickness in Alum Bay of 660 feet, the most important genera being Elfeodendron 

 Taxites, Quercus, Juglans, Daphnogene, Laurus, Caesalpinia, Cassia, Ficus, Dryandra^ 

 Rhamnus and Sabal, &c. They comprise a series of variously-coloured unfossili- 

 ferous sands and clays, with accompanying iron-sandstone and clay. These last 

 beds are in one place crowded with the leaves of sub-tropical land plants illustrating 

 no less than 19 families, 26 genera, and about 50 species : the Araliace<e, Casua- 

 rinacece, Celmtracece, Coniferce, Cornacecp, Cnnoniace(e, Cujndifera, Cycad<e,Ebenace<2 

 Euphorhincece, Jur/landcB, Laurinem, Lef/uminoso', Mor'ece, Pnbnce, Proteacem, 

 Rhamnm, SapindacecB, and Tiliacem. The same strata at Bournemouth and Corfe 

 Castle in Dorsetshire exhibit an identical but also richer flora. Out of the great series 

 found at Bournemouth through the researches of Mr. J. Gardner, fifteen or 

 sixteen species occur in the pipe-clays of Alum Baj'. As a whole they indicate a 

 rather high temperature. The flora of the Lower Miocene beds, well" known in 

 Central Europe, has some affinities with that of our Hampshire basin. 



The tropical or sub-tropical character of the London clay plants was long ago 

 worked out by Dr. Bowerbank, but it was reserved for Dr. Dela Harpeto carry his 

 comparison into the Middle Eocene beds, and to show that there had been only a 

 moderate decrease of temperature, so far as plants could show, in the time occupied ' 

 by the deposition of the Bagshot or Bracklesham sands. The marine fauna of th^ ' 

 same period fully bears out this conclusion, there being no essential difi'erence ' 

 between the fossils of the London clay and those of the Bagshot, or even the 

 Barton beds, which would indicate a marked change of climate. 



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