154 



THYLLITES. 



having been obtained from Stonesfield, a statement which. ther& 

 is no reason to suppose inaccurate. Moreover, the rock appears- 

 to be identical with that in which the majority of the Stones- 

 field plants are found. The available evidence seems to 

 me to point to the identification of this imperfect leaf as 

 a Dicotyledon from rocks of the Great Oolite Series. No trace 

 of an Angiospermous plant has been recognised in the rich Inferior 

 Oolite flora of East Yorkshire, nor has the "Wealden flora, as 

 represented by the plant-beds in the Sussex cliffis, afforded any 

 evidence whatever pointing to the occurrence of Dicotyledonous 

 or Monocotyledonous plants. These facts must of necessity make 

 one very cautious in accepting this somewhat obscure and isolated 

 specimen as proof of the existence of Dicotyledons iu the vegetation 

 which has left fragmentary relics in the Stonesfield beds. 



Assuming that the Stonesfield leaf is that of a Dicotyledonous 

 plant, it is impossible to determine its precise position. The 

 venation characters, so far as they are visible, may be closely 

 matched in the leaves of more than one family of Dicotyledons. 

 I am disposed to think that the best course to follow is to assign, 

 the fossil, with some hesitation, to the convenient genus Phjllites, 

 using the name as a designation for Dicotyledonous leaves which 

 cannot be referred with any certainty to a pai-ticular family. 



I do not regai'd the evidence furnished by the Stonesfield leaf 

 as sufficiently satisfactory to be regarded as furnishing proof of the 

 existence of Dicotyledons during the Jurassic era, but it suggests 

 the possibility that the highest class of plants had made its 

 appearance long before it assumed the dominant position to which 

 it was suddenly raised in the Lower Cretaceous period. Charles 

 Darwin wrote to Hooker in 1879—" The rapid development, as far 

 as we can judge, of aU the higher plants within recent geological 

 times, is an abominable mystery." ' On another occasion he 

 wrote — " Nothing is more extraordinary in the history of the 

 vegetable kingdom, as it seems to me, than the apparently very 

 sudden or abrupt development of the higher plants. I have some- 

 times speculated whether there did not exist somewhere during long 

 ages an extremely isolated continent, perhaps near the South Pole." - 



' Darwin (03), ii. p. 20. 



^ Dariv-in (87), vol. iii. p. 248. 



