160 J. Starkie Gardner — Development of Dicotyledons. 



was being formed over any part of its area, the formation of those 

 qualities of sea-bed called in their upheaved state Gault and Green- 

 sand must also have been forming synchronously over the lesser 

 depths nearer land. 



There is no physical reason whatever why the Aachenian, Danish, 

 Irish, Scotch, or even Devonshire basins or gulfs, should not have 

 begun to form contemporaneously with the deposition of the newest 

 "White Chalk in Kent and Sussex, or even with the much newer 

 chalks that have since been denuded without leaving a trace. Strati- 

 graphy, or rather petrology, is entirely at fault in this question, 

 while paleontology tends to show that subsidence travelled outwards 

 from the South-East of England and the North-East of France, and 

 thaj>-the farther we recede from this centre, the younger will be the 

 r^la1,ive^ ages of the Cretaceous seizes, and the nearer the approach in 

 thenvto what is recognized as a Tertiary fauna. Cretaceous forms 

 wol^ld still be present in the newest of them, for it cannot be sup- 

 ^os^xthat the extinction of these was sudden, or that they must 

 nec^^s^rily be absent from a Cretaceous quality of sea-bed, even 

 thoBgh. its deposition was continued into Eocene times, for much of 

 the life characteristic of the Cretaceous period is even now living in 

 the deeper seas. It would on the other hand be very surprising to 

 find Cretaceous forms in our Eocene muds, as these were formed 

 under wholly different conditions which precluded the possibility 

 of the existence of any faunas approaching in character those of 

 the Chalk. The Aix-la-Chapelle flora, therefore, though overlaid by 

 Greensand and Chalk with some Cretaceous types, is not necessarily 

 as old as it appears to be stratigraphically. In countries so distant 

 as America, we might have had Cretaceous formations in progress 

 pari passu with the formation of our Eocene. The presence of some 

 extinct or supposed extinct types is no certain proof of antiquity, 

 for we only know them to be extinct now, but do not know when 

 they became extinct, because we do not at present recognize the 

 possibility of any deep-sea, or, in other words, deposits of Cretaceous 

 aspect, being of Tertiary age. A great number of Cretaceous genera 

 have been discovered to be not yet extinct ; why then should we 

 suppose that all those that are extinct disappeared simultaneously 

 with the recession of a Cretaceous-depositing sea from our area, in- 

 stead of the more rational hypothesis that they disappeared graduallj^ 

 dropping out now one, now another, at any time between that period 

 and the present day. If these considerations were not lost sight of, 

 we should not find the presence of an Ammonite, Belemnite, or 

 Inoceramus in a deep-sea deposit of America or New Zealand, held 

 as proof conclusive that this is as old as our Cretaceous series, for 

 they may merely be survivals of archaic types, which once swarmed 

 in every condition of sediment, but which gradually took refuge in 

 deeper water, to become extinct, no one can know when until our 

 record of deep-sea deposits be more complete or better understood. 



It is thus obvious that the supposed sudden appearance of a num- 

 ber of highly developed and almost perfectly distinct dicotyledonous 

 floras during the Cretaceous period, at so many distinct parts of the 



