FLORA OF ALUM BAY. 105 



Parana or Kydia, and the detached elytron of a beetle. All bear 

 the appearance of long immersion and tranquil deposition, nnd the 

 sediment is so fine that the disturbance in it caused by the forma- 

 tion and passage of gas bubbles is distinctly visible. Every trace 

 of carbon has been chemically removed. 



This pocket must have been of considerable size, for it was 

 known to Mantell as far back as 1844, and it continued to yield 

 specimens of leaves abundantly down to about 1883, when they 

 became rare, while at present scarcely any vestige of leaf-bearing 

 pipe-clay can be found. 



The number of species obtained from this pocket has been 

 variously estimated. The first critical examination of the flora was 

 by De la Harpe in 1856, when out of 48 species seen, 43 were 

 pronounced determinable and named specifically. Of these 21 of 

 the most important were figured in the former edition of this work. 

 Heer added a species in 1859.* Ettingshausen in 1879 spent 

 a winter in studying collections from Alum Bay, and announcedf 

 that the flora comprised 274 species divided among 116 genera 

 and 63 families. Like Heer, he found considerable afiinity 

 between these and the flora of Sheppey, and further called atten- 

 tion to the community of more than 50 species with the floras of 

 Sotzka and Haring. We are not able to reconcile this estimated 

 richness with our knowledge of the flora, and surmise that 

 fossil plants from other localities must have been inadvertently 

 included. 



The flora appears indeed, very restricted as to species, as we 

 might reasonably anticipate, since we are limited to the leaves 

 which drifted waterlogged into a single pool. The most con- 

 spicuous and typical of these are unquestionably the Ficus Boicer- 

 bankii, De la H., Aralia p'imigenia, Heer, Dryandra acutiloba, 

 Sternb., D. Bunhuryi, De la H., Cassia Ungcri, Heer, and the fruits 

 of Coesalpinia, It is not certain that these determinations are 

 generically accurate, and indeed one of the latest specimens dis- 

 covered proved conclusively that the Dryandra acutiloba is 

 actually a Comptonia ; but they are all well-defined species, and 

 as such form exact bases for comparison. These, with a number 

 of less common but scarcely less conspicuous forms, unite to give 

 the flora of which they are the chief elements, a very special and 

 singularly early impress, so much so that Prof. Newberry would 

 regard them as Cretaceous, if their horizon were not stratigraphi- 

 cally defined. The floras which it chiefly resembles are, firstly, 

 that of Monte Bolca, as already noticed by Heer, and secondly, 

 in a far higher degree, the flora of the Gres du Soissonnais, which 

 though resting on the lignites of Woolwich age in the Paris Basin, 

 are really unconformable and doubtless contemporary with our 

 Lower Bagshot. 



The chief cause of the highly distinctive and interesting 

 character of the Alum Bay flora, lies in the fact that it is the 



* Flora Tertiaria Helvetia;, vol. iii., fol. Wintcrthur. (p. '6lb, Drcpanocarpus 

 Dncampii, Mass.) 



t Proc. Royal See, vol. xxx. p. 228. 1880. 



